Axelsson, G (Department of Environmental Hygiene, University of Gothenburg, Box 33031, S–400 33 Gothenburg, Sweden) and Rylander, R. Exposure to anaesthetic gases and spontaneous abortion: response bias in a postal questionnaire study. International Journal of Epidemiology 1982, 11: 250–256 A postal questionnaire study on anaesthetic gas exposure and miscarriage rate was performed among women who worked or had previously worked in a Swedish hospital. Results were evaluated in relation to age, smoking habits, work site at the first trimester of pregnancy and clinical accuracy of the reported data. An important part of the study was the collection of information on pregnancies among non-respondents. A higher, although non-significant, miscarriage rate was reported among women who had worked in areas with high exposure during the first trimester compared to unexposed women. A selection was found among the non-respondents with respect to both working site during pregnancy and outcome of pregnancy. All women suffering a miscarriage while working at sites with exposure to anaesthetic gases reported their work site and miscarriage, while one third of all miscarriages occurring to women who were not exposed during pregnancy were not reported in the questionnaire.