In 61 patients with end-stage renal disease the results of 89 consecutive Duplex examinations of the arteriovenous fistulas used for haemodialysis were evaluated. The examinations were performed because of various problems concerning the vascular access or before the first puncture. Using 7.5 and 10.0 MHz probes (pulsed Doppler 3.0 and 4.5 MHz) the morphology and the function of the fistulas were evaluated. In 35 cases the results were normal, in a further 27 cases minor anomalies were seen without influencing the function. Complete thrombosis was observed in 7, partial thrombosis and severe stenosis in 4 cases each. Large aneurysms were documented in 6 examinations and in the remaining 6 the fistulas had not matured sufficiently within 4 weeks. The ultrasound results correlated well with consecutive angiography or surgery. The mean flow in normal fistulas was 514 +/- 223 ml/min. It was higher in PTFE shunts (614 +/- 242 ml/min) than in Cimino-Brescia fistulas (464 +/- 199 ml/min). Complications were observed more often in the PTFE group (63.9% vs. 58.5%). We think that Duplex sonography offers an accurate, non-invasive way to evaluate the morphology and the function of arteriovenous fistulas of patients on haemodialysis. This should therefore be performed as the first imaging method whenever problems concerning the fistula occur.