In adult animals with well-established spermatogenesis the testis contains cells of all spermatogenic stages simultaneously whereas the different cell types appear sequentially during the first spermatogenic wave. In this study flow cytometry was used to establish that the first haploid cells (round spermatids) appeared in hamster testes at 24 days post partum (DPP) and mature spermatozoa appeared at 35 DPP. Fixed preparations of testis sections and of cell suspensions obtained from hamsters of ages between 26 and 42 DPP were stained with antibodies reactive with transition proteins 1 and 2. Transition protein 2 appeared first, at 27 DPP and TP1 at 28 DPP.  Confocal microscopy, which allowed correlation of DPP and the steps of spermiogenesis, established that transition protein 2 first appeared at step 6 and TP1 at step 8 of 17 steps. These results are consistent with similar findings in rat, mouse and human spermiogenesis.