The measurement of antibodies specific for the majority of infectious agents in various external secretions is important in the evaluation of potentially protective immune responses at various sites of pathogen entry. Importantly, due to differences in the isotypes of antibodies in various body fluids, levels of total and antigen-specific antibodies in sera and secretions often display independent patterns. The measurement of mucosal antibodies to HIV presents several unique problems. Although controversial, recent results from several laboratories indicate that HIV-specific antibodies are mainly of the IgG and not IgA isotype, despite the pronounced dominance of total IgA in almost all external secretions. Due to the low levels of total IgG in such secretions, highly sensitive methods must be used, including chemiluminescence-enhanced Western blot analyses and ELISA. However, the results generated by ELISA must be interpreted with caution because of a relatively high frequency of false-positive results. Finally, due to the enormous variability of Ig levels not only in various secretions, but also in the same secretion collected at different times, determinations of total Ig levels must be performed to generate meaningful results. © 2009 Humana Press.