Lymphocyte reactivity to group A streptococcal antigens was studied in patients with acute poststreptococcal glomerulonephritis (AGN) in Trinidad. When compared with controls, patients with AGN had significantly lower responses. This finding was most prominent in the patients who were greater than 10 years of age at onset of disease. The total number of T lymphocytes was found to be decreased in patients with AGN, and in particular, the percentage of cells bearing Fc receptors for IgG (T gamma) was low. Removal of the T gamma-cell population abrogated the lymphocyte response to streptococcal antigens. However, removal of the adherent cells resulted in enhancement of the response to the level of the normal control population. The presence of suppressor activity in the adherent cell population of older patients with AGN may be an important factor in progression of AGN to chronic disease.