Lactate dehydrogenase C4 (LDH-C4), the specific isozyme of LDH produced by germ cells, was assessed in the seminal plasma of 55 patients to test a potential link between LDH-C4 and the count per ml of spermatozoa with acrosome anomalies. A simple regression curve shows a statistically significant positive correlation between seminal LDH-C4 concentrations and count per ml of spermatozoa with acrosome anomalies (r = + 0.640, P < 0.0001). No correlation was found between seminal LDH-C4 concentrations and sperm motility. Though seminal LDH-C4 thus seems to be a poor indirect marker of energy produced by spermatozoa, in contrast, this LDH isozyme may be a useful indirect marker of acrosome anomalies.