The possibility of a pharmacokinetic interaction between isosorbide-5-mononitrate (5-ISMN) and epinine, the active metabolite of ibopamine, has been investigated in 8 healthy male subjects given single doses of 200 mg ibopamine and 20 mg 5-ISMN, separately and together. The plasma 5-ISMN concentration-time profile was the same whether 5-ISMN was administered concomitantly with ibopamine or alone [AUC(o-t): 2.24 micrograms.ml-1.h after 5-ISMN alone, 2.16 micrograms.ml-1.h after 5-ISMN+ibopamine]. The plasma concentrations of total and free epinine and the urinary recovery of total epinine, homovanillic acid and dihydroxyphenylacetic acid, too, were not different when ibopamine was administered alone or concomitantly with 5-ISMN. The intake of ibopamine did not change the blood pressure and heart rate. The decrease in diastolic blood pressure induced by 5-ISMN was not influenced by concomitant intake of ibopamine. The observations suggest that in healthy volunteers there is no pharmacokinetic interaction between 5-ISMN and ibopamine.