In order to study the humoral immune defences in the respiratory tract during HIV-1 infection, we measured the levels, local productions and anti-HIV and antibacterial activities of IgG and IgA in the bronchoalveolar lavage fluid (BALF) and serum of 61 adult patients with severe HIV infection and of 56 HIV- controls. Albumin was used as the serum transudation factor. The increase of immunoglobulin levels in the serum of HIV-infected patients was confirmed. The IgG level was also increased in epithelial lining fluid (ELF), whereas the total IgA level was unchanged and secretory IgA (SIgA) level was decreased. The ELF/serum immunoglobulin ratios suggested that the IgG present in ELF resulted mainly from transudation, in contrast to SIgA, which was synthesized locally in controls but greatly diminished in HIV-infected patients. IgG to HIV-1 could be detected in BALF of all the patients, but IgA to HIV-1 only in 30% of patients. BAL IgG reacted more consistently and with a broader array of HIV-1 antigens than did IgA. BAL IgA, when present in samples, reacted primarily with viral envelope antigens. Because IgA specificities to some HIV-1 antigens were detected more intensively by BAL than by serum immunoglobulins, we conclude that the mucosal immune response is distinct from that in serum. IgG antibody activity to Streptococcus pneumoniae was decreased in HIV-infected patients' sera, and IgA antibody activities to S. pneumoniae and to Pseudomonas aeruginosa were decreased in ELF in HIV-infected patients.