Two different common variable immunodeficiency patients were studied. Patient 1 showed hypogammaglobulinemia in all major classes of gammaglobulins and slightly reduced percentages of circulating CD19+ cells, CD20+ cells and surface IgG-or IgA-bearing cells with a normal percentage of surface IgM-bearing cells. Patient 2 showed normal levels in IgM with IgG and IgA deficiencies and almost normal percentages of circulating CD19+ cells, CD20+ cells and surface IgM-, IgG- or IgA-bearing cells. The proliferative responses of peripheral blood mononuclear cells to B cell mitogen, Staphylococcus aureus Cowan I, were reduced in patient 1 but not in patient 2. The intracellular calcium concentrations in lymphoblastoid cell lines (LCLs) transformed by Epstein-Barr virus from patient 2 were increased after anti-mu stimulation. The concentrations were scarcely increased in LCLs from patient 1. These results suggest that B cells of patient 1 have a defective Ca(2+)-dependent signal transduction pathway, resulting in a failure of cell activation and cell proliferation. The defect in B cells of patient 2 may exist on immunoglobulin gene switching or expression rather than the Ca(2+)-dependent signal transduction pathway.