The presence and level of immunoglobulin A (IgA) antibodies to the oral microorganism Streptococcus mutans were determined in human tears, parotid saliva, and serum by a modified, indirect enzyme-linked immunosorbent assay. IgA antibodies were found in the tears of all 15 subjects, although S. mutans is a nonocular bacterium. The IgA antibody levels in tears and saliva were not significantly different. This finding suggests that the level of IgA antibody activity per volume is independent of the naturally occurring site of the antigen, and that local stimulation does not cause a significant difference in the antibody level per volume of secretion between exocrine sites. Much higher levels of IgA antibody were present in serum, suggesting that after oral ingestion of antigen both the systemic and exocrine systems are stimulated. IgG antibodies to S. mutans were also found in human tears, saliva, and serum. No relationship between serum levels and tear and saliva levels was found for either IgA or IgG antibodies. Thus the antibodies in tears and saliva did not appear to have leaked from serum. We conclude that there may be remote regulation of both the ocular and the parotid IgA and IgG antibody systems.