Objective.To study expression and localiza tion of Smad4protein

the common-mediator Smad

which is one of intracellular signaling molecules of transforming growth factor-afamily

in rat t estis during postnatal development.Methods.In this study

whole testes were co llected from S.D rats aged3days

7days

14days and28days

and adult respe ctively.We examined the cellular localization and developmental change of Smad 4in rat testis by immunohistochemical ABC method with glucose oxidase-DAB-nic kel enhancement technique;the quantitative analysis of the immunostaining by t he image analysis system;the Smads pro-teins coexistence in the adult rat test is by the double immune staining for CD14-Smad4and Smad2-Smad4;the prote in expression of Smad during rat testicular development by means of Western blo ts.Results.The protein of Smad4was present in rats from3days of age to adul thood

and the im-munolocalization was exclusively localized to the cytoplasm o f Leydig cells with negative nuclei in the in-terstitial tissue at any time po int.No expression was detected in germ cells.The result of image and sta-tis tical analysis showed that generally

there was a tendency that the expression o f Smad4in the testes increased gradually with the rats developing maturation.C onclusion.Our data provide direct evidence for the molecular mechanism of TGF-aaction in rat testes during postnatal development and spermatogenesis of ra ts.