The immunoglobulin A (IgA)-producing cells in the stroma of major salivary glands are induced by antigenic stimulation of the mucosal immune system. Whether such cells also are induced in minor salivary glands by this stimulation remains to be determined. After application of sheep red blood cells to the palatine tonsils every 3 days for 6 weeks, anti-sheep red blood cell IgA was detected in saliva both by agglutination tests and by enzyme-linked immunosorbent assay. Using enzyme-linked immunospot assay, an increase in the number of anti-sheep red blood cell IgA-producing cells was found in minor as well as in major salivary glands of the sixth week of application; such cells constituted 4.9% to 5.9% of the total number of IgA-producing cells in these tissues. Tonsillar application of whole cells of formalin-killed Streptococcus sobrinus induced anti-S. sobrinus IgA in saliva. The number of anti-S. sobrinus IgA-producing cells in the above glands simultaneously increased over 6 weeks, and reached 5.2-5.6% of the total number of IgA-producing cells.