The present investigation was performed for the purpose of measuring serum immuno-reactive (IR)-beta-lipotropin (LPH), IR-beta-endorphin (EP) and adrenocorticotropic hormone (ACTH) in normal menstrual cycle, pregnancy and labor of normal human subjects. The normal menstrual cycle was divided to menstrual (n = 7), follicular (n = 18), ovulatory (n = 12) and luteal phases (n = 16). The serum concentration of IR-beta-EP and ACTH was significantly higher in the luteal phase than those in other phases. The values for IR-beta-LPH were also higher in luteal phase, but statistically not significant. Normal pregnancy was divided to three groups; I: first trimester (n = 12-15), II: second trimester (n = 11) and III: third trimester (n = 13-18). Normal labor (n = 7) was also divided into two stages, the period with a cervix dilatation of 5cm and 10cm dilatation. The serum concentration of IR-beta-LPH and IR-beta-EP increased progressively with gestational weeks. During labor these two peptides showed maximum values at the period with cervix dilatation of 10cm. These findings indicate that the basic values for opioid peptides in human reproductive cycle can be applied to further clinical analysis of several gynecological disorders.