We previously reported a patients who developed fulminant pneumococcal sepsis 12 years after successful treatment for Hodgkin's disease, which included splenic irradiation. We have since evaluated splenic size and function in 25 patients who had received splenic irradiation 5 to 16 years previously either for Hodgkin's disease (n = 19) or non-Hodgkin's lymphoma (n = 6). Mean maximum splenic diameter as measured on a 99mTc-sulfur colloid liver-spleen scan was 6.2 cm in the irradiated group and 9.7 cm in a control group (p less than 0.001). The mean percentage of erythrocytes containing pits when observed with interference phase microscopy was 13.0% in the irradiated group, which was significantly different (p less than 0.001) from the levels found in each of the control groups: normal subjects, 0.9%; unstaged and untreated lymphoma patients, 0.6%; and patients after splenectomy, 33.7%. Patients who have had splenic irradiation should be considered at risk of developing overwhelming pneumococcal sepsis.