Human T cell clones were derived from peripheral blood and screened for their ability to release gamma-interferon (gamma-IF) following PHA stimulation. Nine clones producing more than 20 U/ml of gamma-IF were expanded and analyzed for cytolytic activity in a lectin-dependent assay and for the ability to release interleukin-2 (IL-2). In addition, clones were analyzed for T4 and T8 antigen expression. Five out of nine clones had cytolytic T lymphocyte activity, while four released relatively large amounts of IL-2. Five clones were T4+ while the remaining expressed the T8+ phenotype. These results clearly indicate that gamma-IF production is not restricted to T cell subsets defined according to either functional or phenotypic criteria.