The effects produced by the administration of aqueous suspensions of the green or dried leaves of Azadirachta indica, a common tropical plant, were investigated in goats and guinea pigs. At doses of 50 or 200 mg/kg given orally over a period of up to eight weeks, the plant produced a progressive decrease in body weight, weakness, inappetence, and loss of condition. There were also decreases in heart, pulse and respiratory rates. Diarrhea was observed in animals given the fresh leaves. In goats, the higher doses of the plant leaves produced tremors and ataxia during the last few days of treatment. No statistically significant hematological changes were observed after dosing the animals with A indica leaves, although there was a tendency towards lowered erythrocyte counts, packed cell volume and hemoglobin concentration. The treatments caused significant rises in the plasma activity of aspartate transferase, sorbitol dehydrogenase, and concentrations of cholesterol, urea, creatinine and potassium. No significant changes in the plasma concentration of sodium, chloride or bilirubin were detected. On necropsy of treated goats there were areas of hemorrhagic erosions. The hearts appeared flappy and in some animals there were hydropericarium. Histopathologically, there was evidence of various degrees of hemorrhage, congestion, and degeneration in the liver, kidney, lung, duodenum and brain. Degeneration of the seminiferous tubules was also seen.(ABSTRACT TRUNCATED AT 250 WORDS)