The immunogenicity and potential for disease modification of pneumococcal polysaccharide vaccine (Pneumovax) in SLE will be evaluated in a controlled, double-blind study. Patients will receive a single intramuscular dose of either vaccine or saline placebo. Anti-pneumococcal antibody concentrations to 12 type-specific pneumococcal capsular antigens will be measured by a radioimmune assay prior to and one and six months following vaccination. The patients will be monitored for clinical and laboratory abnormalities of SLE by a composite clinical, laboratory and serologic index.