Growth factors are involved in the regulation of testicular growth and involution of seasonal breeders. Therefore, we studied the seasonal expression of several growth factors in roe deer: aFGF, bFGF, IGF-1, IGF-2, and TGF-alpha. Total RNA from testis tissue was extracted monthly and analyzed using quantitative RT-PCR. Localization of mRNAs was examined by in situ-hybridization. Levels of expression differed by more than three orders of magnitude. Expression also showed different seasonal patterns. IGF-1, IGF-2 and bFGF were maximally transcribed during testis recrudescence in spring. In contrast, the mRNA amount of aFGF reached its maximum between July (breeding season) and January. TGF-alpha mRNA-levels were very low and showed poor seasonal variation. Each growth factor showed its own typical expression localization in testicular tissues and cell types. The results suggest the specific role of different growth factors in the paracrine control of spermatogenesis and its seasonal regulation.