2,5-Hexanedione (2,5-HD) is a Sertoli cell toxicant that causes irreversible testicular atrophy in rats. After toxicant exposure, only Sertoli cells, stem cells, and a few committed type A spermatogonia remain in the seminiferous epithelium. A majority of the stem cell progeny differentiate into type A spermatogonia, but then, rather than continuing to differentiate, undergo apoptosis. We hypothesized that the cause for germ cell apoptosis was, at least in part, a deficiency in the function of stem cell factor (SCF), a paracrine growth factor normally made by Sertoli cells. To test this hypothesis, rats were exposed to 1% 2,5-HD for 5 wk and killed at various times after toxicant exposure. Northern blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) were used to determine that, unlike what was observed in control testes, the majority of SCF was expressed in the soluble form after 2,5-HD injury. In vitro co-culture experiments were used to establish the appropriate dose of SCF to administer in vivo. A continuous intratesticular delivery system was established and used to expose 2,5-HD-treated rats to SCF for 2 wk. Animals were exposed to bromodeoxycytidine (BrdCyd) for 2 days before being killed in order to assess the effect of SCF on germ cell proliferation. SCF caused a statistically significant increase in the number of germ cells positive for bromodeoxyuridine (BrdUrd), indicating that SCF promoted survival and/or stimulated proliferation of the remaining germ cells. We conclude that SCF expression is disrupted after 2,5-HD-induced testicular atrophy and that exogenous administration of SCF promotes recovery of spermatogenesis.