Subcutaneous (s.c.) administration of delta-9-tetrahydrocannabinol (delta-9-THC) to rabbits produced dose-related cumulative toxicity. Five groups of three New Zealand albino rabbits each received 28 daily treatments with isotonic saline, sesame oil of 15.9, 45.0 or 153.4 mg/kg/day of delta-9-THC dissolved in sesame oil. Dose-related dermal responses included erythema, edema, ulceration and nodule formation. Some of the granulomatous nodules contained an oily substance and exhibited liquefactive necrosis. The severities of erythema and ulceration were generally maximal during the first week of treatment, but edema and nodule formation were most severe after days 12 and 14, respectively. All rabbits survived treatment, but body weights, liver weights and liver glycogen levels were decreased in a dose-related manner. Maximal body weight effects occurred after day 19. Hemochemical changes occurred only in rabbits treated with 153.4 mg/kg/day and included decreased blood sugar and alkaline phosphatase, and increased serum potassium. Hematology parameters were normal throughout the treatment period. No drug-related pathological lesions occurred in internal organs. The cumulative body weight changes, significantly decreased hepatic glycogen levels and reduced blood sugar and alkaline phosphatase values may have indicated drug-induced metabolic changes.