A high performance liquid chromatographic (HPLC) method with both electrochemical detection (ECD) and ultraviolet spectrometric detection (UVD) was developed for the rapid and simultaneous measurement of estradiol (E2), estrone (E1), testosterone (T), 17 alpha-hydroxyprogesterone (17-OHP) and progesterone (P) in serum. These hormones were extracted with diethylether, and chromatographed on an octadecyl silane-silica (ODS) column with an eluent of a phosphate buffer solution - acetonitrile mixture (volume ratio 49:51). Estrogens were detected by ECD at +1.0 V vs. Ag/AgCl, and other hormones by UVD at 242 nm. With this method, the simultaneous determination of sex steroid hormones could be performed within approximately two hours with high precision. The hormones of 34 patients (39 menstrual cycles) undergoing human menopausal gonadotropin (HMG)-human chorionic gonadotropin (HCG) therapy were measured. It was concluded that the switch from HMG to HCG should be performed when the E2 level reaches 400 pg/ml for ovulation and 800 pg/ml for pregnancy. The occurrence of ovarian hyperstimulation syndrome (OHSS) can be predicted when the P level rises above 30 ng/ml on the 7th day after the switch. Moreover, conception may be indicated when the P level does not increase from the 7th to 14th day after the switch. In this way, this method proved to be useful for the monitoring of HMG-HCG therapy.</p