Cultures of human tonsillar lymphocytes stimulated by pokeweed mitogen in the presence of hydrocortisone succinate generate more sheep red blood cell-specific plaque-forming cells than when the hydrocortisone is absent. Such enhancement is even more marked when sheep red blood cells and pokeweed mitogen are present in cultures. This contrasts with the inability of sheep red blood cells to enhance pokeweed mitogen-stimulated response in cultures lacking hydrocortisone. Hydrocortisone causes greater enhancement when the concentration of cells in culture is high than when it is low. These data are consistent with hydrocortisone inhibiting the activity of suppressor cells which would otherwise mask helper effects.