B-cell functions were investigated in a well-defined high-risk group for the development of AIDS/AIDS-related complex (ARC). Stimulation of mononuclear cells (MNC) with T-cell-independent polyclonal B-cell activators failed to increase high spontaneous IgG levels observed in vivo and in vitro. The secretion of IgM following stimulation with Klebsiella M (Klebs M) or Salmonella (Salm) membrane preparation increased by a factor of 4 to 6 and thus ranged between the results of the control group and those of AIDS/ARC patients; the response to a T-cell-independent B-cell mitogen, Staphylococcus aureus Cowan I (SAC), showed profound abnormalities as well in this group. This indicates that functional B-cell abnormalities can be seen in addition to T-cell dysfunctions in patients at increased risk for the development of AIDS/ARC.