Pulegone is a monoterpene ketone that is usually associated with the herb pennyroyal but is also found in the essential oils from many other mint species. It is the major constituent of pennyroyal oil. Pennyroyal is used as a flavoring and fragrance and as an herbal medicine to induce menstruation and abortion. A disposition study of 14C-pulegone in B6C3F1 mice and F344 rats has been conducted at doses from 0.8 to 80 mg/kg. Mice excrete 85 to 100% of the dose in 24 h. Rats excrete only 59 to 81% of the administered radioactivity in the same time, primarily in urine and feces, with a trace in respired air. Consequently, tissue concentrations are lower in mice than in rats. Male rats tend to have higher tissue concentrations, especially in kidney, than female rats have, but this sex difference is not seen in mice. The residual radioactivity at 24 h demonstrates potential for accumulation of pulegone-derived material in several tissues following multiple doses. The metabolic profile is complex in both species, with at least three pathways involving hydroxylation, reduction, or conjugation with glutathione as first steps. Mercapturic acid pathway metabolites were detected in bile in mice and both bile and urine in rats.