Nude rats were injected with human colonic cancer cells (LS 174 T) in the superior mesenteric vein and the extent of hepatic metastases at sacrifice was estimated by visual inspection and computer-based area calculation. After 3 weeks, 5.0 x 10(6) cells caused hepatic metastases in 14/14 rats whereas 0.5 x 10(6) cells failed to produce liver metastases in 4/4 rats (P < 0.001). Injection of 1.0 x 10(7) cells caused portal vein occlusion in 3/5 rats. Extrahepatic tumour growth was rare; lung metastases were observed in four rats, and three rats had local tumour in the abdomen. The average extent of hepatic tumour replacement was 20.2 +/- 4.0%. Injection of embolies or single cells did not affect the incidence or extent of hepatic metastases. The incidence of hepatic metastases was similar in male and female rats, but the extent of hepatic tumour was larger in males (24.6%) than in females (3.2%) (P = 0.005). The pathophysiological similarities to human disease should make this model suitable for diagnostic and therapeutic studies with clinical application.