We compared serum hormone profiles of patients with normal intrauterine pregnancies (n = 14), spontaneously resorbing ectopic pregnancies (n = 10), and viable ectopic pregnancies (n = 26). Hormone profiles were evaluated at 5 to 8 weeks' gestational age. Ectopic pregnancies were diagnosed by laparoscopy; intrauterine gestations were confirmed by ultrasonography. Immunoreactive beta-human chorionic gonadotropin, progesterone, estradiol, and 17-hydroxyprogesterone were measured by radioimmunoassay. Bioactive human chorionic gonadotropin was measured by a modified mouse Leydig cell bioassay. Diminished steroid production was noted in ectopic pregnancies; levels in serum of patients with resorbing ectopic pregnancies were lower than values expressed in viable ectopic pregnancies (p less than 0.01). Serum levels of human chorionic gonadotropin bioactivity correlated closely with immunoreactive human chorionic gonadotropin in all three groups (r = 0.81, p less than 0.01). Ratios of bioactive human chorionic gonadotropin to immunoreactive beta-human chorionic gonadotropin were similar (0.93 +/- 0.26 in resorbing ectopic pregnancies, 1.11 +/- 0.16 in viable ectopic pregnancies, and 0.90 +/- 0.10 in intrauterine pregnancies). We conclude that although reduced serum levels of steroids noted in ectopic pregnancy suggest an impairment in corpus luteum activity, diminished steroid production was not attributable to lower human chorionic gonadotropin bioactivity.