AbstractThe testes, seminal vesicles and coagulating glands of hamsters subjected to bilateral optic enucleation (blinding) involuted within 6–8 weeks. During the first several weeks after blinding there was relatively little change in the weights of the reproductive organs, however, between 4–6 weeks the weights of these organs declined precipitously. Finally, the testes and accessory sex organs of 8‐week blinded hamsters were about one‐tenth and one‐third their normal size, respectively. The atrophic testes exhibited a complete loss of spermatogensis and an apparent diminished secretion of androgens since the seminal vesicles and coagulating glands also regressed significantly. Despite the involution, the testes showed a high degree of deoxyribonucleic acid synthesis as evidenced by the large number of spermatogenic cells which took up tritiated thymidine. These findings indicate that the testes retained a certain level of regenerative capacity even in the presence of advanced tubular damage.If hamsters blinded for 9 weeks, had either their pineal gland or superior cervical ganglia removed, the involuted testes and accessory organs regenerated and returned to the normal size, and presumed function, within approximately 8 weeks. Regenerated testes were histologically indistinguishable from those of normal animals. Eyeless hamsters killed after 17 weeks still possessed involuted reproducti