SummaryThe nitrous oxide and halothane contamination in the inspired air of anaesthetists and in the atmospheres oJ'operating theatres, anaesthetic induction and recovery rooms, were measured during normal unmodified h,orking sessions in 20 hospitals using integrated personal samplers. The nitrous oxide (and halothane) leoels ranged from < I0 to 3000 ppm ( < 0.1 to 60ppm)