The pharmacokinetic properties of 4,4-diphenyl-N-isopropyl-cyclohexylamine-hydrochloride (pramiverine, Sistalgin) in Wistar rats, beagles, and rhesus monkeys are described. After i.v. injection of 14C-labelled pramiverine incorporation of radioactivity from the blood into organs and tissues is rapid. The radioactivity is eliminated from the blood with a half-life of 4-7 h in rats, 17-32 in dogs, and 8-26 h in rhesus monkeys. Unmetabolized pramiverine, in contrast, is eliminated much faster, the half-lives are 2 h in dogs and 3 h in rhesus monkeys. After oral administration maximum serum concentrations are reached after 4 h in rats and dogs and 2 h in rhesus monkeys. The drug undergoes a marked first-pass effect in the liver. In all species pramiverine is absorbed rapidly from the gastro-intestinal tract. Drug and/or metabolites are eliminated in rats and dogs predominantly with feces, in monkeys with urine, independent of the route of administration. During a 6 h interval, biliary elimination was found to be 50% after i.v. and 30% after oral administration. 90% of pramiverine present in the blood plasma is reversibly bound to proteins.