Prosthetic vascular graft infection, though rare, carries high morbidity and mortality rates; therefore, timely diagnosis is important. Patients, however, often present with vague symptoms, and radiological investigations are frequently inconclusive. These factors may lead to prolonged periods of observation and hospitalization, with the resultant increase in costs and complication rates, before reaching a final diagnosis. This prospective study evaluates the use of nonspecific avidin/111In-biotin imaging in diagnosing prosthetic vascular graft infection. METHODS Twenty-five patients with a total of 29 grafts were investigated. Eighteen patients (19 grafts) had low probability of disease, whereas the remaining 7 patients (10 grafts) warranted surgical exploration based on clinical, laboratory or radiological evidence. Avidin was first injected intravenously and then followed 24 hr later by administration of 111In-biotin. Whole-body images were obtained 10 min and 2 hr postinjection of 111In-labeled biotin. SPECT imaging was performed 1 hr postinjection. Increased uptake along part or the whole length of the graft was considered evidence of graft infection. RESULTS Avidin/111In-biotin scintigraphy correctly identified all infected grafts, as confirmed by culturing surgical specimens. In contrast, infection was correctly excluded in all but one of the grafts, and long-term follow-up was used to assess the presence of infection in patients who did not undergo surgical intervention. CONCLUSIONS Avidin/111In-biotin scintigraphy is a simple and accurate imaging method for the routine diagnosis of vascular graft infection, and it may have a role in identifying the disease process in its initial stages, thus improving prognosis.