The effects of a moderate but prolonged exposure of rats to tri-n-butyltin acetate (TBTA) and triphenyltin acetate (TPTA), as might be encountered as residues in yam peel diets, were investigated in rats. These subchronic toxicity studies (16, 8, or 4 mg TBTA/kg and 20, 10 or 5 mg TPTA/kg) showed histopathologic lesions in lungs, liver, intestine and kidney. The hematologic parameters in the groups treated with either compound fell within the normal range for the rats. However, there was a reduction in mean lymphocyte count for rats receiving 10 or 20 mg TPTA/kg, and a reduction in monocyte count in the 20 mg TPTA/kg group. These data indicate a need for further toxicologic studies and cautionary measures to avoid ingestion, inhalation or contamination of dietary materials by these fungicides.