Eight patients with liver metastases from adenocarcinoma of the colon or rectum, two with suspected hepatic metastases and one with primary hepatoma were studied with 2-deoxy-2-[18F]-fluro-D-glucose (18F-FDG) using positron emission tomography (PET). In five of the patients with metastatic tumour a second examination was performed four weeks after treatment with recombinant interleukin-2 (rIL2) and flurouracil (5FU). In all tumours (one primary and eight metastatic) the radioactivity was seen to accumulate in a rim around each tumour with a large central area showing no uptake. In the five cases imaged after treatment with rIL2, the appearance of the tumour uptake was the same as before treatment. In the two cases of suspected but not proven metastases, no abnormal accumulation of18F-FDG was seen.