During pubertal development of the testes, germ cells pass initially through the complete succession of spermatogenic differentiation. Using the golden hamster as a model, this volume presents a comprehensive analysis of that establishing period of mammalian spermatogenesis. Detailed morphological and cell kinetic data of the pubertal seminiferous epithelium reveal a level of cellular organization and synchronization coming near to the adult situation. Characteristic, temporarily occurring perturbations of spermatogenic progression are related to specific delays of Sertoli or Leydig cell maturation, respectively. These results emphasize and specify the close structural and functional interdependence of germ and somatic cell development.