In 1911, the Uruguayan Parliament approved a law of mandatory smallpox vaccination. It was a controversial measure that generated a strong anti-vaccination campaign, led by the naturist movement. Embracing a transcendental understanding of nature, they saw vaccines and surgeries as a threat to the natural balance between body and soul. In this dissertation, I study how Uruguayan naturists positioned themselves as a secular alternative to science that combined reason and spirituality, and I show how they had a documented impact on the local political and scientific culture. By focusing on a country with a distinct anti-clerical tradition, I bring to the fore how apparently contradictory phenomena like secularity and spirituality overlap. The spirituality imbricated in their idea of nature, I conclude, resulted in conservative political gestures, even within progressive movements. Among many other things, they embraced a language of purity and sacredness around the body, both human and animal, that led them to the opposition to vaccinations, surgeries and meat consumption, which they regarded as violent moral transgressions. The influence of naturism in the country has not yet been sufficiently considered, and my research presents a first approach to a central aspect of the intellectual life of the period. Besides being a popular movement, it influenced key political, scientific and cultural figures, who, in turn, shaped laws, scientific policies and the elite’s understanding of science and its possibilities. To demonstrate this, through a cultural studies perspective, and in dialogue with science and technology studies and medical humanities, I do close-readings of an unexplored archive of naturist and theosophist periodicals, pamphlets and books published in the first two decades of the 20th century. I also study more well-known anarchist publications and philosophical works by prestigious medical doctors, such as Mateo Legnani (1884-1964), and Carlos Santín Rossi (1884-1936), both close to naturism, focusing on how they also represent an alternative body of knowledge where scientific thought and spirituality coalesce. I conclude by studying essays by the Spanish-Paraguayan writer Rafael Barrett (1876-1910), who debated with the Uruguayan naturists and wrote illuminating pieces on the issue. To this end, I structure the dissertation in three chapters. In the first one, I discuss the political impact of naturism and argue that the movement’s opposition to the 1911 law of compulsory smallpox vaccination highlighted the Government's tendency to subordinate individual freedoms, a fundamental principle of the newly formed liberal state, to what they saw as the common good, which contradicted the Government’s modernizing discourse and agenda. Moreover, naturists formulated some well-founded systematic critiques of the political values imbricated in academic medicine. By pointing this out, I challenge the opposition between them and university trained physicians, the latter historically represented as defenders of science and reason, and the former as religious fanatics. Indeed, the public health paradigm adopted by medical authorities appealed to nature in a very similar way than naturists did. Several renowned medical doctors, some of them parliamentary representatives, without openly identifying themselves as such made direct references to naturists’ precepts in their books and in public documents, including law bills. The second chapter revolves around the vision of science developed by naturism and its political and epistemological implications; there, I argue that while naturists amplified the metaphysical elements present in the history of medicine, from vitalism to Neo-Hippocratism and romanticism, such spiritual views remained compatible with the anticlericalism that characterized the Uruguayan society. I study two iterations of the movement that represent different understandings of science and that reveal specific political and philosophical tensions present in Uruguayan society. One of them, led by Antonio Valeta (1882-1945), proposed an accessible version of science, highlighting the autonomy of the individual. He appealed to values of freedom and personal effort that were part of the liberal imaginary and came into tension with the centrality of the state and its reformist agenda. The second one was developed by Fernando Carbonell (1880-1947), a member of the Theosophical Society and other esoteric groups. His vision was informed by a sophisticated system of beliefs, composed of mystical and conceptually dense metaphysical, ethical and aesthetic teachings that led to valid epistemological criticisms to the model of laboratory science that was being embraced by the authorities. In the third and final chapter, elaborating on the fact that naturists and other groups across the political spectrum mobilized a secular spirituality inherent to the idea of nature, I posit that this led to conservative political positions, even within progressive movements and individuals that were attracted to naturist precepts. Indeed, naturism explicitly opposed actions that could be considered revolutionary in favor of a gradual evolutionism, appealing to the same principle of non-violence embraced in their vegetarianism. In turn, they elevated the philosophical and metaphysical purity of the defense of the life of all beings above the actual living conditions of people and human suffering, romanticizing poverty and illiteracy as states closer to nature. To conclude, my dissertation brings attention to the diversity of belief systems and values still at stake in the present-day scientific landscape. Current iterations of naturism, as illustrated by the anti-vaccination movement both in Uruguay and internationally, resort to claims and arguments eerily similar to those developed more than 100 years ago in Montevideo and other parts of the world. Now, as they did in the past, activists advocate for individual freedom and against the intervention of foreign substances that alter the natural balance of their bodies. Moreover, within the context of the coronavirus pandemic, scientific discussions are taking over the public sphere in an unprecedented way, echoing past dynamics where public figures denounced scientists as biased and despotic elitists who wanted to subject the people to their arbitrary regulations.