From the Department of Anaesthesia, Alberta Children's Hospital at the University of Calgary, Calgary, Alberta.This paper was presented in part at the Canadian Anaesthetists' Society Annual Meeting in Ottawa, June 1989.Address correspondence to: Dr. C. Wood, Department of Anaesthesia, Alberta Children's Hospital, 1820 Richmond Road SW., Calgary, Alberta.Accepted for publication 15th May, 1992. Contamination of the operating theatre with trace concentrations of waste anaesthetic gases is an inevitable consequence of the use of inhalational anaesthetic agents. The health risk to operating theatre personnel resulting from chronic exposure to trace concentrations of these agents has been the subject of numerous studies during the last 20 yr. Among the agents studied, the toxic effects of nitrous oxide have been the focus of much attention. Horace Wells first demonstrated the anaesthetic properties of nitrous oxide in 1844, but it was not until 1956 that the first adverse side effects from its use were reported. In that year, Lassen described bone marrow surpression in patients sedated with nitrous oxide for long-term ventilation) Since then, possible adverse effects on bone marrow, psychomotor function, and reproductive function have been described. 2-8 This has led to concerns regarding possible ill effects from the chronic occupational exposure CAN J ANAESTH 1992 / 39:7 / pp 682-6