Metabolism of ibopamine (N-methyldopamine-O,O'-diisobutyryl ester) was studied in rats and dogs. The compound was well absorbed in both species when given orally. Most of the administered radiolabel (74-94%) was excreted within 24 hr in urine of both species. The major metabolite in rat urine was 4-glucuronylepinine (63% of the total administered dose). Minor metabolites identified were 4-O-glucuronyl-3-O-methylepinine, 3,4-dihydroxyphenylacetic acid (DOPAC), DOPAC-glucuronide, homovanillic acid (HVA), and HVA-glucuronide. Free epinine and epinine sulfate were detected in the range of less than 1% of the total administered dose. Metabolite patterns in dog urine were different from those of rat urine. The major metabolite was epinine-3-O-sulfate (62% of the total administered dose). Minor metabolites identified in dog urine were DOPAC-sulfate, HVA-sulfate, and free HVA. Free epinine was detected but in the range of less than 1% of the total administered dose. These results showed that ibopamine underwent extensive hydrolysis in vivo to epinine, which was subsequently conjugated and excreted as major metabolites in urine. In addition, side chain degradation of epinine led to minor metabolites, which were excreted in urine as free and conjugated forms. The route of conjugation of ibopamine metabolites is species dependent.