We examined age-related changes in the expression of transforming growth factor-β(1) (TGF-β(1)) and transforming growth factor-β(2) in mouse testes. The mice were assigned to three age groups: 35, 50, and 75 days old. Paraffin embedded testis sections were processed for the standard streptavidin biotin peroxidase complex immunohistochemistry method. TGF-β(1) expression increased in aging round spermatids over the time studied. There was no expression in 35-day-old Leydig cells, whereas strong expression of TGF-β(1) was observed in 50-day-old Leydig cells. Expression decreased in 75-day-old Leydig cells. TGF-β(2) expression was weak in 35- and 50-day-old mouse spermatids, but expression was greater in 75-day-old elongated spermatids. In Leydig cells, TGF-β(2) expression was strong in both 35- and 50-day-old mice, whereas the expression of TGF-β(2) was less in 75-day-old Leydig cells. Our results suggest that TGF-β(1) and TGF-β(2) may play significant roles in testicular functions and germ cell development in mice.