Induction of theophylline-sensitive T-suppressor cells with THF, a thymic hormone, resulted in elevation of the low levels of these lymphocytes in non-treated asthmatic children. Evaluation, however, by monoclonal OKT8 antibodies did not show changes in the levels of the OKT8+ cells after THF incubation. In the treated asthmatic children, normal levels of theophylline-sensitive T-suppressor cells as well as OKT8+ cells were found. These normal levels were not changed with THF after in vitro incubation.