The general pharmacological properties of 1-(m-methoxyphenyl)-2-(dimethylaminomethyl)-cyclohexan-1-ol (tramadol; Tramal) are described and compared with those of other strong narcotic analgetics. In behavioral studies tramadol in high doses had a primarily stimulating effect in mice and rats and a sedative effect in rabbits and dogs. The Straub tail phenomenon, a reaction typical for mice administered morphine, was observed only after subtoxic doses of tramadol. In i.v. doses tramadol generally caused a weak central inhibition of non-stimulated and electrically stimulated brain activity in unanesthetized rabbits. Muscle tone and motor coordination in rats and mice were only slightly affected by the drug, in contrast to the effect of morphine. Unlike other strong analgesics tramadol in doses of 5--20 mg/kg i.v. did not cause respiratory depression and even clearly increased respiratory volume and rate in conscious rabbits and anesthetized dogs. In cats and dogs i.v. doses of tramadol up to 10 mg/kg were well tolerated in the cardiovascular system. Tramadol has a slight, papaverine-like spasmolytic effect and no effect on gastrointestinal motility or urinary and electrolyte excretion. The drug showed no antipyretic properties in rabbits. It inhibited edema in rats and guinea pigs but had no antiproliferative effect in the cotton pellet test in rats. Tramadol did not inhibit monoamine oxidase activity or cause enzyme induction in the rat liver.