The MRL-lpr/lpr (MRL/l) mouse spontaneously develops an autoimmune disease associated with various rheumatic manifestations. We have studied the histological features of sialadenitis and utilized an immunohistochemical staining technique on frozen tissue sections to analyse the cellular composition of the salivary glands at varying stages of disease. Semiquantitative assessment of the infiltration disclosed a focal inflammation which started at 2 months of age and was progressive until 5 months of age in submandibular glands. A high frequency of Ly-1 and L3T4-positive cells was observed at all stages of sialadenitis, whereas Lyt-2 positive cells were found at a lower frequency. Ia expression was seen on a large proportion of the infiltrating cells and also on ductal and glandular epithelial cells in the vicinity of the inflammatory lesions. The presence of Ia antigens on many inflammatory as well as resident cells and the high frequency of lymphocytes with 'helper' phenotype may indicate a perpetuated immunological activation within salivary glands.