AbstractWe examined the effect of famotidine, a histamine-type 2 receptor antagonist, on the immunocompetent cells. The number of DR(+)cells were significantly decreased in patients with systemic lupus erythematosus (P<0.05) by parenteral administration of famotidine (40 mg/days for 4 weeks). However, total lymphocyte number and monocyte number did not change. Immunoglobulin levels of patients with rheumatoid arthritis and normal male did not change. Furthermore, phytohemmaggulutinin induced lymphocyte proliferation was increased by addition of famotidine (10 ng/ml). Nonetheless, famotidine did not have raitogenic function itself to lymphocyte and did not affect IL-2 product ion.