SUMMARYThe sedative and toxic properties of morphine, and five semi-synthetic opiates (diamorphine, dihydromorphinone, dihydrocodeine, oxymorphone and oxycodone) have been determined by giving them, in a double-blind trial, as pre-anaesthetic medication to a standard female population. Diamorphine and dihydromorphinone produced the best sedation whilst dihydrocodeine was least efficient in this respect. Dihydromorphinone and oxymorphone were markedly more toxic than the others, whilst dihydrocodeine was the least toxic drug in this group.