[en] During recent years, Rao et al. (1991) using a mouse model and intratesticular injections of several radionuclides, have shown that the spermatogonial damage is greater with Auger-emitting radionuclides compared with long-range β-emitters. This paper provides experimental evidence that the ^114mIn radionuclide can not only gain access to the spermatogenic epithelium in its so-called 'pharmacological sanctuary' within the seminiferous tubules, but can also bind to the mutagenically sensitive spermatid population at certain stages of their development. (author)