Our current investigations include the determination of the heterogenicity of lymphocyte populations in the regional lymph nodes from animals undergoing Herpes corneal infections. Preliminary experiments involved rabbits with acute corneal dendritic keratitis. Regional lymph nodes were harvested after days three, five, seven and ten, and prepared in single cell suspension. An aliquot was removed for "whole" lymph node cell suspension testing and the remainder was placed on a twenty through thirty percent bovine serum albumin step gradient. After centrifugation, clearly defined layers were observed. Less dense cells near the top of the gradient were labelled Fraction A, and those with increasing density were labelled B, C, and D respectively. All fractions were tested against two specific T cell mitogens, PHA and Con A; a less selective mitogen, pokeweed; as well as specific Herpes antigens. Non stimulated cultures and appropriate controls were included. Indeed, "differential" responses to the selected mitogens and specific Herpes antigens were observed. Utilizing Stimulation Index as a criterion, we observed a linear increase in response to Herpes antigens by the whole lymph node cell suspension increasing with time after infection; a "potentiated" response by Fraction A on day seven and a "potentiated" response by Fraction C on day 10. Utilizing H3 Thymidine Incorporation (i.e. blast transformation) as a criterion, we observed that a highly "potentiated" response of different fractions of regional lymph node cells to T cell mitogens and specific Herpes antigens serves as a basis for monitoring "potentiating" and "suppressive" factors associated with various populations of lymph node cells.