Young tadpoles of Bufo bufo, with genital ridges filled with primordial germ cells at the beginning of mitotic proliferation, were subjected to 400r X-ra y panirradiation and were cultured, for the histological examination, until 25 days after the end of metamorphosis. At this developmental stage, their Bidder organs always showed several residual germ cells, which had normally reached bidderian oogenesis. Their gonads, on the contrary, often appeared completely lacking in germ cells. However, in the cortical and medullary somatic tissues of these sterile gonads the sex differentiation had normally occurred and, as a consequence, the female or male sterile gonads appeared quite differently organized. A precocious destruction of germ cells does not therefore modify the somatic sex differentiation of the gonads.