Nonsmoking females age 35-65 years from Bremen, Germany (91 women), and Opole, Poland (98 women), were interviewed about their recent passive smoking exposure. We obtained urine samples at the time of interview and determined the concentration of cotinine as an indicator of tobacco smoke exposure. In Poland and in Germany, the vast majority of nonsmoking women are involuntarily exposed to environmental tobacco smoke (ETS). Polish women had slightly higher exposure levels than German women, with overall means of 9.93 and 8.65 ng cotinine/mg creatinine, respectively. Smoking by the husband was the major source of exposure in both study groups. In the Polish group, the work place was also an important source of ETS exposure. The validity of self-reported passive smoking exposure was found to be generally good; it was somewhat better in the German study group. A negative attitude toward tobacco smoke was slightly stronger among the German women. The percentage of women misreporting their active smoking status was low.