Morphological observations of male genital tracts obtained from wild, adult Mexican big-eared bats (Corynorhinus mexicanus) revealed only one but long annual reproductive cycle showing the existence of temporal asynchrony of its reproductive functions, as is characteristic of temperate-zone vespertilionid and rhinolophid chiropterans. Testes were largest in August, whereas maximum development of epididymides and accessory sex glands complex was observed 1 and 3 months later. High value of relative body condition of individuals was observed from May to June, when testicular enlargement commenced, suggesting that recrudescence of spermatogenesis in the adult bats is dependent on a good body condition.