Nicocodine is an opioid related to codeine. It is also an antitussive agent. Nicocodine exhibits at least twice the potency of codeine in clinical experiments. The study of the pharmacokinetic behaviour of nicocodine by means of blood and brain level curves of rats after i .v. application showed that the penetration of the blood brain barrier seems to be favoured for nicocodine. The detected peak concentration of nicocodine in brain after i.v. application is 4.4 times higher than the blood level values at the same time - codeine the main metabolite is detected in almost equal amounts in brain and blood. A comparative assay of codeine and nicocodine after p.o. application of equimolar doses per kg body weight revealed that predominantly codeine is found in brain and its peak value after nicocodine administration is 3-fold higher than after codeine administration. Nicocodine is hydrolysable to morphine and the WHO Expert Committee on Addiction-Producing Drugs (1962) recommended its international control as a narcotic, like other convertible drugs in the morphine series.