27 cases of ectopic pregnancies (gestational period: 44 +/- 5d) and 33 cases of normal pregnancies (gestational period: 44 +/- 5d) as control groups were studied in our hospital from November, 1992 to May, 1994. The levels of serum hormone (beta HCG, E2, P) were measured in two groups by a radioimmunological method. The results were compared. The values of beta HCG, E2, and P in ectopic pregnancy group were significantly lower than in the control group (P < 0.01). The E2/P levels in ectopic pregnancy group were significantly higher than in the control group (P < 0.01). Our conclusion is that ectopic pregnancy may be due to the state of the higher E2 levels.