Pregnant mice of C57BL/6 and DBA/2 inbred strains were exposed to cigarette smoke during days 1-18 of pregnancy. Both mothers and offspring were killed at the age of 21-22 weeks, and ovaries were studied with respect to the number of primordial follicles and small primary follicles. In additional studies, 7,12-dimethylbenz(a)anthracene (DMBA) was administered on day 15 of pregnancy. Cigarette-smoke exposure during gestation did not affect the number of primordial follicles in the ovaries of mothers, whereas counts were significantly decreased (31%) in the ovaries of DBA/2 offspring, and decreased, although not significantly (20%) in the ovaries of C57BL/6 offspring. DMBA (5 to 50 mg/kg) decreased oocyte counts in the mothers in a dose-dependent manner. At the same doses, DMBA reduced the viability of the offspring. These studies suggest that primordial and small primary follicles may be more sensitive to components in cigarette smoke during fetal life than in adulthood.