A standard operative procedure and anaesthetic technique were employed in a comparison of eight intravenous barbiturates which were used as the main anaesthetic in combination with nitrous oxide and oxygen. Series were premedicated with either atropine alone or pethidine and atropine. There was little difference between the clinical effects of equipotent doses of thiopentone, thialbarbitone, thiamylal and Inactin. Hexobarbitone caused a very high incidence of muscle movements and hypotension, and was the worst of the drugs studied. Both buthalitone and methitural were associated with excessive respiratory upset. Methohexitone alone showed clear advantages over standard compounds. Complete clinical recovery was quicker and there was less tendency to depress blood pressure