Immunoglobulin G subclass responses to lipoarabinomannan (LAM) of Mycobacterium tuberculosis were determined by ELISA in both HIV-1 antibody positive (n = 31) and negative (n = 43) patients with tuberculosis (TB). Responses were also studied in a group of healthy controls (n = 16) and HIV-1 antibody positive (n = 60) individuals without TB. IgG2 antibodies were the predominant subclass, being present in 25 of 43 non-HIV-infected TB patients (58%) and in 11 of 31 HIV-infected TB patients (35%). However, HIV+ TB patients also showed IgG4 (n = 16; 52%), and IgG1 (n = 4, 13%) responses to LAM, whereas these subclasses were absent in sera from HIV-TB patients. Individuals in both non-tuberculous control groups showed no antibody responses to LAM. The influence of HIV infection on B cell responses to LAM, and possible mechanisms for antibody-mediated regulation of immunity to TB, are explored.