Gentamicin (GM)-induced nephrotoxicity limits the use of this antibiotic. It has been shown that aged garlic extract (AGE) and S-allylcysteine (SAC), the most abundant organosulfur compound in AGE, ameliorate GM-induced nephrotoxicity in rats. The present communication evaluated the effect of AGE and SAC on proliferation and on GM-induced toxicity and genotoxicity of porcine kidney epithelial cell line (LLC-PK1 cells). The cells were preincubated with different concentrations of AGE or SAC for 12 h before incubation with 8 mm GM for an additional 72 h. At the end of this time, cell viability, genotoxicity and proliferation were evaluated. AGE stimulated cell proliferation and protected LLC-PK1 cells from GM-mediated toxicity and genotoxicity. SAC partially prevented only GM-induced genotoxicity. These results suggest that the stimulation of cell proliferation could possibly be one of the mechanisms involved in the in vitro protective effect of AGE in GM-induced toxicity of LLC-PK1 cells.