Current imaging modalities are unable to detect small liver metastases because of limited resolution and contrast differentiation. The association between liver metastases and altered liver blood flow has been demonstrated by dynamic scintigraphy, but the clinical feasibility of this test has been questioned. In this study a novel approach to detecting liver metastases was assessed by measurement of liver blood flow using a duplex/color Doppler System. Hepatic arterial and portal venous blood flows were measured in 16 controls, 50 patients with gastrointestinal cancer, and 6 patients with breast cancer. The ratio of hepatic arterial to total liver blood flow (Doppler perfusion index, DPI) and the ratio of hepatic arterial: portal venous blood flow (Doppler flow ratio, DFR) were calculated. The DPI and DFR values of controls and patients with overt liver metastases were clearly separated (p less than 0.0001). The results suggest that duplex/color Doppler ultrasound measurement of hepatic perfusion changes may be of value in the detection of liver metastases.