SummaryTotal lactate dehydrogenase (LDH), LDH‐X, creatine phosphokinase (CPK) activities and ATP content were measured in washed spermatozoa from 188 normospermic and 94 oligozoospermic men. These four biochemical parameters were significantly higher (p>0.00l) in spermatozoa from oligozoospermic men than in those from normospermic men and were related inversely to sperm concentration. In oligozoospermic men the activity of sperm LDH and LDH‐X was related sipficantly to sperm CPK activity (r = 0.5486 and r = 0.4442, respectively), whereas this relationship was less evident in normospermic men (r =0.4124 andr= 0.3844, respectively). Sperm ATP content was related weakly to sperm LDH, LDH‐X and CPK activities both in oligozoospermic and normospermic men. After separation on a discontinuous (40% and 80%) Percoll gradient LDH, LDH‐X, CPK activities and ATP content in 80% separated sperm fractions from 48 normospermic and 30 oligozoospermic men were found to be significantly lower than in the initial semen sample in both groups of subjects. The 80% separated sperm fi‐actions fiom oligozoospermic and normospermic men did not differ in their LDH or LDH‐X activities or ATP content, whereas sperm CPK activity was still significantly higher in oligozoospermic men. These data suggest that, of the four parameters studied, high levels of intracellular CPK activity are the most relevant biochemical feature of spermatozoa from oligozoo