Splenic function as measured by number of vacuolated red blood cells (RBC) seen with phase contrast microscopy was studied in 44 patients with systemic lupus erythematosus (SLE). Two of 44 patients (4.6%) had increased percentages of vacuolated RBC (8.4% and 30.6%) indicative of hyposplenism. Both patients had inactive disease at the time, were on low doses of corticosteroids, and had persistence of vacuolated RBC when restudied 2 and 4 months later. The present study confirms the association of hyposplenism with SLE and indicates that the incidence of hyposplenism in SLE is about 5%.