Results are reported for air sampling surveys undertaken by the Health and Safety Executive (HSE) from 1980 to 1984 using diffusive samplers in 40 operating theatres and 18 recovery areas at 27 hospitals. For all personnel the geometric mean time-weighted average exposure to nitrous oxide in unscavenged theatres was 94 ppm and in scavenged theatres 32 ppm; the corresponding means for halothane were 1.7 and 0.7 ppm, respectively. Intermittent use of scavenging led to mean exposures between those found in scavenged and unscavenged conditions. Anaesthetists showed higher mean exposures than other staff in all conditions. Statistical analysis of the data demonstrates that mean exposures of operating theatre staff were significantly lower in scavenged than in unscavenged theatres. For most staff, exposure was also significantly lower in theatres using active scavenging systems compared with those using passive systems. The literature on the hazards of chronic exposure to inhalation anaesthetics and previous studies of exposure is also briefly reviewed.