The cytokine TNFalpha is known to be secreted by testicular germ cells. However, its effect on maturing germ cells is unknown, and its role in the regulation of spermatogenesis is unclear. Here we aimed at characterizing the effects of TNFalpha on germ cell survival in the human testis. We found that TNFalpha effectively and dose-dependently inhibited germ cell apoptosis, which was induced in vitro by incubating segments of human seminiferous tubules under serum-free culture conditions. EMSAs indicated increased activity of nuclear factor kappaB in seminiferous tubules cultured under apoptosis-inducing conditions. However, we did not observe any significant effect of TNFalpha on the activation of this transcription factor, which is often considered to be a mediator of TNFalpha-induced survival signals. As the expression of the TNF receptor protein in the human seminiferous epithelium was predominantly found in the Sertoli cells, the antiapoptotic effect of TNFalpha is probably mediated via these somatic cells. Interestingly, expression of the Fas ligand, a known inductor of testicular apoptosis, was down-regulated by TNFalpha. Thus, in the seminiferous tubules, germ cell-derived TNFalpha may regulate the level of the Fas ligand and thereby control physiological germ cell apoptosis.