The evidence that chronic exposure to inhalational anaesthetic agents may be associated with psychomotor, hepatic and renal dysfunction, to increased susceptibility to infections and neoplastic disease, and to an increased incidence of miscarriages and foetal abnormalities, is discussed. The risk to pregnant women seems greatest after exposure to rather high concentrations of nitrous oxide. Although it is not suggested that all laboratory premises will be equally at risk, such levels as 400 ppm halothane and 8000 ppm nitrous oxide can build up in small poorly ventilated rooms when these agents are used for several hours at a time. A strong plea is entered for all to be aware of the hazard and to ensure that good ventilation and preferably, purpose-built scavenging equipment are installed wherever inhalational agents are used.