The epidemiological literature on the ocupational hazards of anaesthesia which includes some sort of control data has been studied. It provides reasonably convincing evidence of a moderate increase in the risk of spontaneous abortion among exposed females, although it is possible that even this result is attributable to reporting bias. There is no convincing evidence of any other hazard. It has been pointed out by many authors that, even if spontaneous abortion is commoner among those working in anaesthesia, there is no particular reason to believe that this has anything to do with exposure to trace quantities of anaesthetic gases. The special emotional and physical rigours of the task, for example, might easily be responsible.