Patients with non-Hodgkin's lymphomas who failed to respond to chemotherapy were treated with low dose fractionated total body irradiation (TBI). Prior to during and after scheduled therapy, their clinical status was evaluated and peripheral blood studies were performed to enumerate EAC and E rosetting cells and to measure proliferative responses to mitogens. Peripheral blood abnormalities were present prior to TBI using these in vitro assays. Patients who obtained clinical remissions following therapy had restoration of mitogen progressive disease had no change in their ability to proliferate in response to mitogens. Normalization of EAC and E rosetting profiles often occurred regardless of clinical response. These data indicate that low dose fractionated TBI produces clinical and in vitro detectable immunological changes. Furthermore, they show that improvement in mitogen responsiveness correlates best with good clinical responses.