In 1991, an outbreak of Pseudomonas cepacia bacteremia (PCB) occurred among patients at an oncology clinic in Alabama. A case-patient was defined as any patient at Alabama Oncology Hematology Associates (AOHA) who had at least one blood culture positive for P. cepacia from 7 August through 31 October. Fourteen case-patients were identified; all required hospitalization (median duration, 17 days), but none died of PCB. A cohort study assessing risk factors for PCB focused on all patients who had been treated on the 8 days when case-patients had last visited AOHA during the period 7-21 August. Only patients with central venous catheters developed PCB (P < .001). Among patients with central venous catheters, PCB occurred only after visits to AOHA at which the catheters were flushed with heparin solution in the AOHA laboratory rather than in the treatment area (P < .001). P. cepacia was cultured from the only intravenous fluid bag used to prepare heparin flush solution in the laboratory during the interval 7-21 August. All outbreak-associated isolates of P. cepacia had an identical DNA ribotype pattern. These findings emphasize the importance of avoiding multiple use of single-use solutions, especially for high-risk patients with long-term indwelling central venous catheters.