The IgA anti-EBV (Epstein-Barr virus) response during the course of IM (infectious mononucleosis) was investigated. The IgA anti-VCA (viral capsid antigen) response was found not to be restricted to the early acute phase of the EBV infection as is the IgM anti-VCA response. Some patients with normal total serum IgA levels did not respond with measurable EBV specific IgA. These patients and those with low titers of IgA anti-VCA had shorter duration of sore throat than responders with high titers indicative of a strong correlation between the IgA anti-VCA titers and the duration of sore throat. In this way the EBV specific IgA response is unique since recent observations show that local oropharyngeal symptoms during IM appear poorly synchronized with the IgM and the IgG antibody responses. As EB virus is excreted into the oropharynx during IM, antigens are available for local EBV immunization. The results of the present study imply a possible local immunization process as a positive correlation was found between serum IgA anti-VCA and total salivary IgA.