Leukocyte-endothelial cell (EC) interactions regulate the entry of immune effectors into the tissues. This interaction occurs in lymphoid tissues and inflammatory sites at post-capillary high endothelial venules, as opposed to large capacitance vessels lined with flat EC. Transient SV40 infection of mouse EC derived from lymph node stroma has resulted in a cell line, SVEC4-10, that retains morphological and functional characteristics of normal EC. SVEC4-10 cells grow efficiently on plastic as a monolayer with a characteristic epithelioid morphology. They require as little as 2% FCS and are independent of other exogenous growth factors or matrix components. When grown on a synthetic basement membrane, SVEC4-10 forms branching tube-like networks. SVEC4-10 expresses Factor VIII related Ag as measured by indirect immunofluorescence using a rabbit antiserum to human FVIII-associated protein and incorporates acetylated low density lipoprotein. SVEC4-10 specifically binds mouse lymphocytes in vitro. IFN-gamma induces expression of MHC class II Ag in a time course identical to normal EC and the cell line is susceptible to lysis by anti SV40 H-2k CTL clones. Thus, this SV40 immortalized line retains much of the normal cellular physiology of EC.