Patients receive oral thalidomide in a blinded, placebo-controlled study. [AS PER AMENDMENT 11/25/98: This is a double-blind, placebo-controlled trial in which thalidomide or placebo is administered for 21 days. After the first week of therapy, patients receive immunizations with keyhole limpet hemocyanin and polyvalent pneumococcal vaccine. Study therapy is stopped for 2 weeks after the immunizations. Following the immunizations, detailed evaluations of the immune responses to the vaccines are conducted over the next 8 weeks.]