1. (+/-)-[methyl-14C]-Hydratropic acid was administered to man, rhesus monkey, cat, rabbit and fruit bat. 2. All species excreted 60-100% of administered 14C in the urine in 24 h, and unchanged hydratropic acid accounted for 0-17% of the dose. 3. In man, the urinary 14C consisted of a very small quantity (1%) of unchanged hydratropic acid with the remainder as hydratropylglucuronide. 4. Hydratropylglucuronide was the major urinary excretion product in the 4 animal species, while the glycine conjugate was present in the urine of cat and rat. Additionally, cats excreted the taurine conjugate of hydratropic acid. 5. Bile-duct cannulated rats excreted 20-30% of an injected dose of [14C] hydratropic acid in the bile in 3 h mainly as hydratropylglucuronide.