In this study we investigated the expression of the immediate early genes (IEGs) c-fos, c-jun, and junD on mRNA and protein levels during the spermatogenic cycle of the rat using Northern blotting, in situ hybridization, and immunocytochemistry. The expression of these IEG mRNAs and proteins exhibited stage-specific variations. The results suggest that IEGs take part in transcriptional events that are involved in regulating the proliferation and differentiation of spermatogenic cells during specific stages of the cycle of the seminiferous epithelium.