Exposure of male mice to 6 Gy of X-rays resulted in a very rapid and extensive sloughing of the germinal epithelium as shown by the accumulation of nonsperm cells within the lumen of the epididymis. These cells were identified as stage 1 and 2 round spermatids. After accumulating in the caput, they progressed through the epididymis over the weeks of sampling and, by Week 9 after irradiation, they had completely disappeared from the organ. It is suggested that the precocious loss of round

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... ids is responsible for the induction of oligospermy within the testis and the caput epididymidis. Similar sperm losses from the cauda epididymidis were not observed. Radiation also enhanced the frequency of misshapen spermatozoa normally found in this strain. From kinetic considerations, it is suggested that the generation of abnormal spermatozoa may be biphasic with an early component comprising maturing spermatids and a late contingent composed of affected spermatocytes. Return to the pre-irradiation level of abnormal frequency was not observed within the time frame of this study (10 weeks), perhaps indicating residual damage. The synchrony that existed among the various organs in terms of both sperm loss and the generation of abnormal spermatozoa may be the result of a rapid dispersion of gametes from the testis and not due to local responses as would be expected if sperm flow were affected by the irradiation. The distribution of abnormal sperm types was different in the testis from that in the epididymis, presumably because of a testicular spermatophagic mechanism specific for the removal of certain deformities. It is concluded that the kinetics of spermatogenesis, of spermiogenesis, and of sperm transport in the mouse is not affected by exposure to 6 Gy of X-rays.