Through a qualitative analysis of the use of intestinal parasites for treating immune system disorders, this research illustrates how contingency emerges in the context of the human relationship to hookworms. The affect of the human–nonhuman relationship is an important part of understanding the direction of evolutionary medicine today, and has implications for the politics of biological health innovations. The shift from the bad parasite to a parasite that at least sometimes heals, discursively and materially, has opened new spaces for patients to change the way they relate to medical knowledge, medical professionals, and pharmaceutical companies. Hookworms are banned by the FDA, which sets the scene for lively, but sometimes rebellious, hybridity between host and parasite. Underground and do-it-yourself hookworm therapy cultures have sprung up in around the site of the gut. I argue that not only is material hookworm affect as important as human discourses in negotiating the rapidly advancing field of biome reconstruction, but it also plays a role in how that biome reconstruction takes place, conventionally or otherwise.