1-Isothiocyanato-3-(methylsulphinyl)-propane (IMSP or iberin) is one of the major glucosinolate hydrolysis products found in cruciferous vegetables. The toxicity of IMSP after oral administration is unknown. This study examined the histological lesions and serum biochemical alterations resulting from intragastric administration of IMSP to male Fischer F344 rats. Rats were administered IMSP in corn oil by gavage at concentrations of 0.1, 0.3, 0.6, 1.0 and 2.0 mmol/kg body weight. Rats were anaesthetized and exsanguinated, and perfusion fixed at 4, 24 and 72 hr after dosing. IMSP caused a dose-dependent decrease in body weight for the first 24 hr after dosing. Multifocal haemorrhages and erosions of the mucosal portion of the stomach were grossly and histologically evident after 4 hr in rats dosed with more than 0.3 mmol IMSP/kg body weight, with severity increasing with dose. Mucosal lesions resolved by 72 hr in all but the 2 mmol/kg group. No significant lesions were observed in the liver or kidney. No physiologically significant haematocrit, electrolyte, blood urea nitrogen, creatinine or serum enzyme activity changes were observed. Urine collected after a dose of 1 mmol IMSP/kg body weight accounted for 1% of the IMSP, demonstrating that the compound was absorbed from the gastro-intestinal tract.