10 lymphoma patients given a total of 26 courses of intravenous continuous infusion of recombinant interleukin-2 (rIL-2) alone without lymphokine-activated killer cells were analysed retrospectively for the frequency and pattern of bacterial infections associated with the immunotherapy. 4 episodes of septicaemia and 7 episodes of soft tissue infections resulted from the 26 courses of rIL-2 infusion. Although there was no death due to infection, all these infections were clinically significant, needing systemic antibiotic therapy and resulting in prolonged hospitalisation. Gram-positive infections occurred significantly (p less than 0.001) more often than gram-negative infections. Patients with non-Hodgkin's lymphoma had a higher incidence of infection than patients treated for Hodgkin's disease, analysed either as infection per patient treated (p less than 0.05) or infection per course of rIL-2 given (p less than 0.02).