Abstract Potassium picloram was administered either by gavage (acute studies) or in drinking water to male and female Sprague-Dawley-derived rats (14-day and 90-day studies). The acute oral LD50 was 950 mg/kg (812–1120) for males and 686 mg/kg (599–786) for females. Depression, prostration, ataxia, tremors, and convulsions preceded death. There were no consistent biologically significant compound-related effects in rats that received 60, 190, or 600 mg potassium picloram/kg/day for 14 days. In the subchronic study, rats received 60, 190, 600, or 1070 mg potassium picloram/kg/day in drinking water for 90 consecutive days. There were only 4 male and 2 female survivors out of 20 rats of each sex at the 1070 mg/kg dose and 16 male and 18 female survivors at the 600 mg/kg dose. Mortality was dose dependent. Administration of picloram appeared to exacerbate renal and hepatic lesions commonly noted in rats of this age. For example, at levels up to 1070 mg/kg mild lesions in the kidney of treated rats, especially in males at 600 mg/kg, were noted. Also noted were an increased incidence of mononuclear liver foci in male rats that received 190 and 600 mg/kg and an increased severity of mononuclear liver foci in females that received 600 mg/kg. There were no other consistent biologically significant compound-related effects. No specific organ site toxicity could be identified in these studies. Toxicity from exposure to picloram in drinking water is apparently low.