The prevalence and titers of antibodies to capsid antigens of Epstein-Barr virus ad to the diffuse and restricted components of the Epstein-Barr virus-induced early antigen complex were determined in 109 families of a semirural community in Louisiana. Titers of antibody to the capsid antigens larger than or equal to 10 were found in 84 percent of children aged two to five years, and the prevalence increased with age to nearly 100 percent. There was a positive but variable correlation of the prevalence of anti-capsid antigen reactivity with low socioeconomic status and crowding. An overrepresentation of high titers of antibody to capsid antigens was present in individuals with a past history of pneumonia and urinary tract infections. The geometric mean titers of antibody to capsid antigens were highest in early childhood, lowest in adolescence and young adulthood, and high in the elderly. Females in all age groups and tonsillectomized children showed a higher geometric mean titer than their male and nontonsillectomized counterparts, respectively. Antibodies to the early antigen complex were found rarely (8.2 percent) and only in sera with relatively high titers of antibody to capsid antigens.