OBJECTIVE To access beta-endorphin levels in serum as well as seminal plasma in different infertile male groups. METHODS Beta-endorphin was estimated in the serum and seminal plasma by enzyme-linked immunosorbent assay (ELISA) method in 80 infertile men equally divided into four groups: non-obstructive azoospermia (NOA), obstructive azoospermia (OA), congenital bilateral absent vas deferens (CBVAD) and asthenozoospermia. The results were compared to those of 20 normozoospermic proven fertile men. RESULTS There was a decrease in the mean levels of beta-endorphin in the seminal plasma of all successive infertile groups (mean +/- SD: NOA 51.30 +/- 27.37, OA 51.88 +/- 9.47, CBAVD 20.36 +/- 13.39, asthenozoospermia 49.26 +/- 12.49 pg/mL, respectively) compared to the normozoospermic fertile control (87.23 +/- 29.55 pg/mL). This relation was not present in mean serum level of beta-endorphin between four infertile groups (51.09 +/- 14.71, 49.76 +/- 12.4, 33.96 +/- 7.2, 69.1 +/- 16.57 pg/mL, respectively) and the fertile control group (49.26 +/- 31.32 pg/mL). The CBVAD group showed the lowest seminal plasma mean level of beta-endorphin. Testicular contribution of seminal beta-endorphin was estimated to be approximately 40%. Seminal beta-endorphin showed significant correlation with the sperm concentration (r = 0.699, P = 0.0188) and nonsignificant correlation with its serum level (r = 0.375, P = 0.185) or with the sperm motility percentage (r = 0.470, P = 0.899). CONCLUSIONS The estimation of beta-endorphin alone is not conclusive to evaluate male reproduction as there are many other opiates acting at the hypothalamic pituitary gonadal axis.