The concentrations of human chorionic gonadotropin and prolactin in the cyst fluid of molar tissue were compared with that of normal amniotic fluid. Molar fluid was aspirated from the vesicles of molar tissue in eight women (duration of amenorrhea 14.1 +/- 1 week, mean +/- SEM). Amniotic fluid was obtained at amniocentesis in 24 women (mean duration of amenorrhea 15.9 +/- 0.2 week). Hormones were measured by specific radioimmunoassay. The concentrations (mean +/- SEM) of human chorionic gonadotropin in molar fluid and amniotic fluid were 581,829 +/- 112,581 and 3187 +/- 505 mlU/ml (p less than 0.001), respectively. For prolactin the levels in molar fluid and amniotic fluid were 44 +/- 24 and 1962 +/- 313 ng/ml (p less than 0.001), respectively. These data demonstrate that molar fluid contains 182-fold higher levels of human chorionic gonadotropin and 45-fold lower levels of prolactin than amniotic fluid obtained from normal pregnant women with a similar duration of amenorrhea. In addition to altered endocrine function of the trophoblast, there may be altered prolactin secretion from the decidua in molar pregnancy as compared with normal pregnancy. Further research is required to evaluate prolactin production from decidua of molar pregnancy.