Successful antiretroviral (ARV) treatment is associated with suppression of HIV viral load and the reduction of clinical disease progression. Despite marked improvements in ARV medication, side effects from long-term treatment, such as loss of muscle mass do occur. The mechanism by which ARVs affect muscle mass is unclear, however, published in vitro data suggests a negative effect on myoblast fusion during differentiation. The objective of this study was therefore to determine the effect of ARVs on processes required for successful myogenesis; these included proliferation, migration during wound repair, and differentiation. C2C12 mouse skeletal myoblasts and human primary culture skeletal (HSk) myoblasts were incubated with Zidovudine (nucleoside reverse transcriptase inhibitor-NRTI), Tenofovir (nucleotide reverse transcriptase inhibitor-NtRTI) or Ritonavir (protease inhibitor-PI) at a concentration range of 0.01 μM to 10 μM. Proliferation was determined using crystal violet and migration was analyzed using a 2D wound healing assay. The commitment of myoblasts into the myogenic lineage was assessed via the expression of the transcription factor Pax7. Differentiation was measured by assessing the fusion index of multinucleated myotubes. C2C12 myoblast proliferation was observed to increase significantly in response to Tenofovir (1 μM and 10 μM). In HSk cells however, proliferation was observed to decrease significantly in response to Tenofovir (1 μM). Zidovudine had no consistent effect on C2C12 proliferation at any dose tested, but caused a decrease in HSk myoblast proliferation (0.01 μM and 0.1 μM); however this was statistically non-significant. A small dose-dependent increase in C2C12 and HSk cell number, although not significant, was seen in response to Ritonavir. Wound closure results revealed both dose-dependent and time-dependent effects of Tenofovir and Zidovudine on human myoblast migration, with significant decreases in the rate of wound closure (4-7 hours) noted at 0.1 μM and 0.01 μM doses respectively. Zidovudine had no significant effect on migration while Ritonavir (0.01 μM) was observed to significantly increase percentage wound closure of human myoblasts, suggesting an increased ability to migrate during wound repair. Differentiation results indicated a decrease in myoblast fusion in response to all three ARVs. However only Ritonavir was shown to negatively affect myosin heavy chain expression. Further research into the exact mechanism of decreased fusion is required. To our knowledge, this study is the first to suggest that selected ARVs may significantly influence myoblast regeneration capabilities by modulating myoblast proliferation, migration, differentiation and fusion, and thereby decrease their myogenic capability. Extended human myoblast studies on differentiation could confirm this hypothesis. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2013.