A 53-year-old white man had fever, malaise, and dyspnea on exertion. His chest roentgenogram was normal, but pulmonary function tests showed impaired diffusion capacity and a gallium scan showed marked uptake in the lungs. Results of an open-lung biopsy documented Pneumocystis carinii pneumonia. Immunologic test results were consistent with the acquired immunodeficiency syndrome. The patient denied having homosexual contact or using intravenous drugs. Twenty-nine months before the diagnosis of pneumocystis pneumonia was made, the patient had had 16 transfusions of whole blood, platelets, and fresh-frozen plasma during coronary artery bypass surgery at another medical center. This patient is not a member of any currently recognized high-risk group and is believed to have contracted the acquired immunodeficiency syndrome from blood and blood-product transfusions.