An increasing number of research studies in men indicate endurance exercise training has significant effects upon the major male reproductive hormone, testosterone, and the hypothalamic-pituitary-testicular axis that regulates reproductive hormone production. This review article addresses a relatively new reproductive endocrine dysfunction found in exercising men, what has been deemed the exercise-hypogonadal male condition. Specifically, men with this condition exhibit basal (resting-state) free and total testosterone levels that are significantly and persistently reduced. The exact physiological mechanism inducing the reduction of testosterone is currently unclear, but is postulated to be a dysfunction (or perhaps a readjustment) within the hypothalamic-pituitary-testicular regulatory axis. The time course for the development of the exercise-hypogonadal condition or the threshold of exercise training necessary to induce the condition remains unresolved. The potential exists for these reduced testosterone levels within the exercise-hypogonadal male to be disruptive and detrimental to some anabolic or androgenic testosterone-dependent physiological processes. Regrettably, few research studies have addressed whether such processes are affected; thus, findings are equivocal. Conversely, the alterations in circulating testosterone brought about by endurance exercise training have the potential for cardiovascular protective effects and could be beneficial to the health of these men. Present evidence suggests this condition is limited to men who have been persistently involved in chronic endurance exercise training for extended periods of time (i.e., years) and is not a prevalent occurrence. Nonetheless, many questions regarding the male reproductive endocrine adaptive process to exercise training still remain unanswered, necessitating the need for much further research.