A biomarker can be broadly defined as any biological index capable of being measured, which is associated with or indicative of a defined biological endpoint such as a developmental or disease stage. Various biomarkers of reproductive development and health have been identified, including those associated with pubertal development and adult reproductive health. Herein we discuss those in situ biomarkers which have been more closely associated with the reproductive system. In males these are primarily associated with altered spermatogenesis and sperm parameters with altered endocrine function. Current understanding of the role of mitochondria in disease is expanding rapidly, and it is now clear that mitochondrial dysfunction is responsible for a wide variety of disorders. Little attention has been paid to mitochondrial disorders in germinal tissues. However, several recent reports have considered the possibility that mitochondrial dysfunction could be implicated as a factor in male infertility. In particular, some evidence suggests that mitochondria could play a key role in the energy maintenance of spermatozoa motility, one of the major determinants of male fertility. However, biochemically defined alterations of these respiratory chain activities are usually associated with all kinds of mitochondrial disorders. The target of this study was to investigate the correlation between ultrastructural changes and mitochondrial succinate dehydrogenase enzyme activities in infertile & fertile human spermatozoa. The results obtained strongly suggest that an Ultrastructural change largely depends on the whole energy production originating in the mitochondrial enzymes compartment. We have found a close and positive relationship between Ultrastructural and mitochondrial enzyme specific activities, suggesting that more specific mitochondrial dysfunctions could be the underlying cause of idiopathic male infertility. The immunocytochemical assessment of mitochondrial enzymes in sperm samples of idiopathic infertile individuals could help to identify cases of mitochondrial-based asthenozoospermia.