Objective To investigate time-dependent changes of serum proteins permeability inthe normal and cadmium(Cd)-treated mouse testis, reflecting tight junctional (TJ) barriersof Sertoli cellsMethods The serum proteins, albumin and immunoglobulin-G(IgG), in the seminiferoustubules were firstly immobilized by the "in vivo cryotechnique", in which the dynamicblood circulation was always kept. The cryofixed testicular tissues were then processedfor the freeze-substitution method, and embedded in the paraffin wax. Serial sectionsof 5μm thickness were immunostained by anti-mouse albumin or IgG antibody withperoxidase immunostaining, and also stained with hematoxylin-eosine (HE)formorphological observation.Results In normal seminiferous tubules, albumin immunoreaction products werelocalized around peritubular myoid cells and among Leydig cells, as well as in bloodvessels. They were also localized as arch-like patterns around some spermatogonia inbasal compartments. The number of the immunopositive arch structures was differentaccording to developmental stages of the seminiferous cycle, judging from thearrangement of germ cells by HE-staining. The patterns of localization of IgGimmunostaining in normal mouse testis were similar to that of albumin. In 24 h afterCd-treatment, some enlarged spaces and vesicular formation in the seminiferousepithelium were observed on the paraffin sections by HE-staining. The albumin or IgG immunolocalization was seen not only in the basal compartments, but also in theadluminal compartments between Sertolicells and germ cells.Conclusion The structural changes of inter-Sertoli TJ barriers in vivo, such as differentimmunostaining patterns of serum proteins between the normal and Cd-treated mouseseminiferous tubules, could be clearly detected by the "in vivo cryotechnique" withalbumin or IgG immunohistochemistry.