Hypergammaglobulinemia and defective humoral immunity are hallmarks of HIV-1 infection. Naive B cells have been recently suggested as the major source of hypergammaglobulinemia in chronic viral infections. We recently reported that HIV-1–infected patients carry low levels of memory B cells. Here we studied whether defects in the naive and memory B cells in HIV-1–infected patients translated into hypergammaglobulinemia and defective humoral immunity against specific antigens. Naive B cells from HIV-1–infected patients exhibited abnormal expression of the activation/differentiation markers CD70 and leukocyte-associated Ig-like receptor (LAIR-1). Activated naive B cells from patients showed a significant increase in the intracellular immunoglobulin G (IgG) content ex vivo and this activated phenotype correlated to hypergammaglobulinemia and to the ability of naive B cells from patients to secrete IgG in vitro. We analyzed the levels of antibodies to tetanus toxoid, measles, and HIV-1 in relation to memory B cells and observed a significant reduction of antigen-specific antibodies in patients with low-memory B lymphocytes. Nevertheless, hypergammaglobulinemia and levels of polyspecific self-reactive antibodies were comparable in patients with normal and low memory B cells. We conclude that reduction of memory B lymphocytes in HIV-1 infection correlates with defective humoral immunity and that hyperactivated naive B cells may represent the source of abnormal IgG production in HIV-1 infection. Our results may be relevant to the design of HIV-1 therapeutical vaccines and to the clinical management of HIV-1–infected patients.