During a 2-year period 5 previously healthy young men who had undergone splenectomy and received multiple transfusions for trauma had severe cytomegalovirus (CMV) infection. Their illness was characterised by a long period of high fever, severe interstitial pneumonitis with dyspnoea and hypoxaemia, and an unusually high lymphocytosis (12 000-26 000 cells/microliter) with numerous atypical forms. The presumptive diagnosis was based on the patients' seroconversion and viral excretion, on the clinical and haematological findings which were typical of severe CMV infection, and on the absence of other infective organisms. In 1 case widespread CMV pneumonitis was confirmed at necropsy. These observations raise the possibility that splenectomy increases the severity and modifies the pattern of CMV infection, since during the same period no other case of severe CMV infection was observed among a large number of patients who had received multiple transfusions but had not undergone splenectomy.