A survey was undertaken to evaluate the possible relationship between spontaneous miscarriage and exposure to the operating room. The study was carried out by personal interview of 67 operating room and 92 general duty nurses. Results indicate that during the years 1966–1970, 29.7 per cent of pregnancies in operating room nurses ended in spontaneous miscarriage, compared with only 8.8 per cent in the control group. A similar pattern was observed in a second study of 50 anesthetists and 81 physicians practicing in specialties other than anesthesia. During the six-year period 1965–1970, the anesthetists evidenced a 37.8 per cent spontaneous miscarriage rate, compared with 10.3 per cent in the control group. Miscarriages occurred earlier in both operating room nurses and anesthetists compared with their control groups (eighth versus tenth week). These results suggest a fetal lethality, possibly due to the anesthetic gases, although the studies do not incriminate any specific anesthetic agent, nor is a cause-effect relationship established.