Until now, little attention has been paid to the contribution of mitochondrial dysfunction to germinal tissue disorders. The target of this study was to investigate the relationship between sperm motility and mitochondrial respiratory chain enzyme activities. The results obtained showed that semen samples of control individuals (n = 33) have substantially higher activities of complexes I, II, and IV compared with those of asthenozoospermic subjects (n = 86). Moreover, a direct and positive correlation was found in the whole population studied between spermatozoa motility and all the mitochondrial respiratory complex activities assayed (I, II, I+III, II+III, and IV). The ratio of these enzymes to citrate synthase (a reliable enzymatic marker of mitochondrial volume) activities did not correlate with sperm motility. This suggests that motility depends largely on the mitochondrial volume within the sperm midpiece. These observations could be of physiopathological relevance because they suggest that factors affecting the mitochondrial energy production could be then responsible for particular cases of idiopathic asthenozoospermia.