To determine the ability of antiretroviral treatment (ART) to deter viral replication in the long term, we tested autologous neutralization of HIV-1 primary isolates in sera from six chronically HIV-1-infected patients before and during such treatment. For comparison, heterologous neutralization was tested in the same samples by using a panel of eight primary HIV-1 isolates. Preceding ART, none of the patients' samples contained neutralizing antibodies against autologous HIV-1 isolates. Subsequently, despite successful ART treatment during a 12- to 19-month period and a rise in CD4 T cell counts, the patients' viral neutralizing capacity did not increase significantly. Furthermore, the partial heterologous neutralizing response was not improved in these patients. This outcome signifies the failure of an HIV-1-specific humoral immune response to improve, despite successful ART. Therefore, our results emphasize the need for immunologic intervention before cessation of ART in chronically HIV-1-infected patients to achieve sustainable control of viral replication.