Concentrations of 3 alpha-androstanediol (A) and 3 alpha-androstanediol glucuronide (AG) were measured with a radioimmunoassay in pregnancy plasma samples collected from the mother in the first trimester (first, n = 18) and second trimester (second, n = 20) and at term (n = 14). At term, along with the maternal samples, matching cord plasma samples were also obtained (n = 14). Throughout pregnancy the levels of A and AG were significantly higher than in normally menstruating women. Although the total concentration of A and AG did not change significantly throughout pregnancy, the levels of A in the second and at term were significantly higher than in the first. In contrast, AG concentrations in the second were significantly lower than in the first and at term. As compared to the maternal concentrations at term, the cord levels of AG and A plus AG were not significantly different. However, the levels of A in the cord were significantly lower than those in the maternal circulation at term. Significant correlations were observed between the term maternal and cord levels of AG and A plus AG. No sex-related differences in the plasma levels of A and AG were noted. The results show that levels of A and AG increase significantly in the first trimester and remain elevated throughout pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)