We used in situ hybridization to study the expression of interleukin genes in sarcoidosis and in persistent generalized lymphadenopathy of HIV disease. In both cases, we found a dramatic over-expression of the interferon-gamma (IFN gamma) gene as compared to that of the interleukin-2 (IL-2) gene. In sarcoidosis, IFN gamma producing cells are CD4 T cells and are associated with IL-1 beta gene expressing monocytic cells. In HIV lymphadenopathy IFN gamma producing cells are C8 T cells engaged in cytotoxic function, as evidenced by the concomitant expression of serine esterase B gene. Thus distinct patterns of interleukin production can be defined in vivo in selected immunopathological situations.