There is evidence that exposure to environmental factors is at least partly responsible for changes in semen quality observed over the past decades. The detection of reproductive toxicants under Registration, Evaluation and Authorisation of Chemicals (REACH) will impact animal use for regulatory safety testing. We first validated a model of culture of rat seminiferous tubules for toxicological studies on spermatogenesis. Then, using this model of culture, we assessed the deleterious effects of 1, 10, and 100 μg/l hexavalent chromium [Cr(VI)] on meiotic cells. The prophase I of meiosis was studied in vivo and ex vivo. Bromo-2′-deoxyuridine (BrdU) was used to describe the kinetics of germ cell differentiation. SCP3 labeling allowed to establish the distribution of the stages of the meiotic prophase I and to perform a qualitative study of the pachytene stage in the absence or presence of Cr(VI). The development of the meiotic step of pubertal rats was similar in vivo and ex vivo. The number of total cells appeared not affected by the presence of Cr(VI) irrespective of its concentration. However, the numbers of late spermatocytes and of round spermatids were decreased by Cr(VI) even at the lower concentration. The percentage of synaptonemal complex abnormalities increased slightly with the time of culture and dramatically with Cr(VI) concentrations. This model of culture appears suitable for toxicological studies. This study shows that Cr(VI) is toxic for meiotic cells even at low concentrations, and its toxicity increases in a dose-dependent manner.