Abstract The spontaneously developing sialadenitis in female autoimmune NZB × NZW F 1 ( NZB W ) mice has been studied with the help of immunohistochemistry and monoclonal antibodies to cell surface antigens. Semiquantitative assessment of stained cells within the infiltrates disclosed a progressive focal inflammation most pronounced in subman-dibular and parotid glands. The majority of cells expressed Ly-1 (all T cells) and L3T4 (T helper) phenotype, whereas only few Lyt-2 (cytotoxic/suppressor) expressing T cells were seen. A large proportion of the infiltrating cells stained for Ia antigens, which was also found on salivary gland ductal epithelium in the proximity of lymphoid infiltrates. The phenotypic pattern in sialadenitis of NZB W mice thus closely resembles the pattern previously described for human Sjögren's syndrom (SS). Accordingly, immunomorphological analysis of the NZB W sialadenitis may be useful in further studies of pathogenesis and therapy of both experimental and human SS.