Endorphins and β-lipotropin have been implicated as the modulators of pain during the labor process. To investigate their possible role during parturition, the present study was undertaken to determine the levels of β-endorphin, β-endorphinlike immunoactivity, and β-lipotropin during labor and delivery. Fourteen patients were evaluated at 4 cm dilatation, complete dilatation, at the time of delivery, and immediately postpartum. In addition, samples were obtained from nine nonpregnant control subjects. The venous levels of β-endorphinlike immunoactivity and β-lipotropin were determined, and the β-endorphin level was calculated. The maternal cerebrospinal fluid (CSF) levels and the newborn umbilical venous level also were determined in the delivery room. A gradual rise was noted in the β-endorphin, β-lipotropin, and β-endorphinlike immunoactivity values up to the time of delivery. There was noted to be a modest decrease in their levels in the immediate postpartum period. These levels were significantly elevated over control samples for both β-endorphinlike immunoactivity and β-lipotropin (P< .05). Values for β-endorphin were not significantly different from control levels. In addition, maternal CSF levels were found to show modest elevations above the simultaneously drawn venous specimens. The umbilical cord venous samples drawn at delivery were also higher than the simultaneous maternal venous levels. These values, although elevated over control values, were not statistically different from simultaneously drawn maternal venous levels.