The specificity and polyreactivity of the antibody response in natural HIV-1 infection were studied. First, to investigate the overall antibody response, overlapping linear peptides were used to screen sera taken from HIV-1-infected individuals. The polyclonal antibody response was relatively stable during long-term infection, compared with acute infection, and mostly directed against immunodominant regions. Low level, transient antibody responses were detected against membrane proximal external region of gp41. To test if these antibodies are neutralizing, an affinity purification method was developed to isolate these serum antibodies. Second, in terms of polyreactivity of antibody response, we found that two broadly-neutralizing monoclonal antibodies bound only weakly to self antigen, cardiolipin. Moreover, sera were screened against cardiolipin; no significant reactivity was observed. We conclude that the antibody response in HIV-1 natural infection is relatively stable over time; the MPER is weakly immunogenic in vivo, and that broadly-neutralizing antibodies do not seem to be autoreactive.