Abstract
Cryptorchid testes from adult mice were incubated in calf serum-supplemented medium. There was an effective differentiation of adult type A spermatogonia up to the pachytene stage of meiotic division which resembled the process of spermatogenesis in vivo. In the absence of calf serum, type A spermatogonia did not differentiate at all. They differentiated when the serum was present for the 1st day, but was absent for the rest of cultivation. Serum is necessary for only the early process of spermatogenesis from type A spermatogonia in vitro and not for the further processes of germ cell differentiation. Type A spermatogonia cultured in serum-free medium retained the ability to differentiate for at least 3 days.