Both meiotic and postmeiotic maturation events have been observed to occur in human male germ cells during in-vitro culture. The temperature of 30 degrees C, medium supplementation with follicle-stimulating hormone and testosterone and the maintenance of the original cell-cell associations within explanted segments of the testicular seminiferous tubules are common features of the most efficient culture systems. The in-vitro maturation processes are markedly accelerated as compared to the in-vivo situation, probably due to the abrogation of a checkpoint controlling the full assembly of molecules needed for spermiogenesis. Moreover, both meiotic and postmeiotic maturation processes can be reactivated in vitro in some cases with a complete block of the same processes in vivo. Healthy babies were born after micromanipulation-assisted fertilization with in-vitro matured elongated spermatids from men with complete in-vivo maturation arrest at the round spermatid stage and at the primary spermatocyte stage.