Genital ridges of Bufo bufo tadpoles at different stages of development were cultured in vitro for 15-20 days. The results were: 1) the in vitro preservation of germ cells is good for protogonia and oogonia, less good for diplotenic oocytes and even less forsynaptic oocytes; 2) larval oogenesis in Bidder's organ does not start in vitro, but it prosecutes if already begun at the explantation moment, as shown by meiotic changes of cultured oogonia; 3) gonadic tracts of cultured genital ridges are able to begin sex differentiation in vitro.