The ability of lymphocytes from a patient suffering from the acquired immune deficiency syndrome (AIDS) to produce interleukin-2 (IL-2) was found to be comparable to that of his healthy sex partner and to that of a normal control. Addition of exogenous IL-2 to lymphocyte cultures did not improve the poor mitogen response to phytohaemagglutinin in this patient. Our data suggest that the underlying defect in this AIDS patient is due to an IL-2 receptor defect.