[en] The effects of high LET radiations produced with accelerated heavy-ion beams on weight loss of the mouse testes have been examined. It is assumed that weight loss is due primarily to cell death in the germinal epithelium. Results indicate that little or no recovery of sublethal injury occurs in this cell renewal system. Generally, the RBE rises continuously and monotonically for all LET values associated with helium and carbon from 6 to 100 keV/μm. On the other hand, the data for neon and argon do not appear to fit. From the standpoint of the radiobiology of heavy ions, the most significant observation is that LET alone does not account for variation in radiation response of the spermatogonial population