A six-month study was conducted in p53(+/-) mice to evaluate the possible oncogenicity of resveratrol (3,5,4'-trihydroxy-trans-stilbene), a cancer chemopreventive agent present in grapes and other foods. p53(+/-) mice (25/sex/group) received daily gavage exposure to vehicle only (negative control), resveratrol doses of 1000, 2000, or 4000 mg/kg/day, or p-cresidine (400 mg/kg/day; positive control). No mortality was seen in mice receiving the low dose of resveratrol. However, the mid and high doses induced mortality associated with impaction of the test article in the gastrointestinal tract. Resveratrol had no effect on body weight, food consumption, or clinical signs in surviving mice in any dose group, but induced dose-related increases in liver weight and serum cholesterol in both sexes. Mild anemia was seen in male mice at the high dose only; hematologic effects were not seen in females. Histopathology identified the kidney (hydronephrosis) and urinary bladder (epithelial hyperplasia) as target tissues for resveratrol toxicity. The incidences of both benign and malignant tumors in mice exposed to resveratrol were comparable to those in vehicle controls. By contrast, the positive control article, p-cresidine, induced urinary bladder cancer in both sexes. When administered to p53(+/-) mice at its maximum tolerated dose, resveratrol demonstrates no evidence of oncogenicity.