Female rats were exposed by inhalation to trichloroethylene (TCE) vapors at a concentration of 1800 +/- 200 ppm to determine whether exposure before mating and during pregnancy is more detrimental to reproductive outcome than exposure either before mating alone or during pregnancy alone. Four treatment groups were utilized in a two by two factorial design: exposure to TCE for 2 weeks before mating and during the first 20 days of pregnancy; TCE before mating and filtered air during pregnancy; filtered air before mating and TCE during pregnancy; and filtered air before and during pregnancy. Significant elevations in skeletal and soft tissue anomalies, indicative of developmental delay in maturation rather than teratogenesis, were observed in the group exposed during pregnancy alone. The mixed function oxidase enzymes, ethoxycoumarin and ethoxyresorufin, indicative of cytochrome P-450 and P-448 activities, respectively, were measured in maternal and fetal livers, as well as livers of non-pregnant females, and showed variable levels of activity not uniformly related to treatment or pregnancy. Behavioral evaluation of offspring indicated a lack of treatment effect in tests of general activity levels at 10, 20 and 100 days of age. However, a reduction in postnatal body weights was seen in offspring from mothers with pregestational exposure. No results indicative of treatment-related maternal toxicity, embryotoxicity, severe teratogenicity or significant behavioral deficits were obtained in any of the treatment groups.