Background: Thymidylate synthase (TS) has been associated with clinical outcome in disseminated colorectal cancer. However, many patients with low TS expression still fail to respond to treatment. Therefore, we studied the cell cycle proteins, Rb, E2F2, Ki67, p21 and p53 and the apoptotic proteins, mcl-1, bax, bcl-xl, bcl-2, Fas receptor, Fas ligand, caspase-3, M30 and PARP as potential predictive factors. Patients and methods: In biopsy specimens of liver metastases from 31 colorectal cancer patients, protein expression was retrospectively determined by immunohistochemistry and related to response to hepatic arterial or intravenous (i.v.) 5-fluorouracil (5-FU) treatment, time to tumour progression (TTP) and overall survival. Results: Expression of both p53 and Rb correlated with survival benefit after 5-FU treatment. A median survival time of 79 weeks was found in patients with high levels of p53 or Rb compared to 36 and 44 weeks for patients expressing low levels of p53 (P = 0.027) or Rb (P = 0.030), respectively. Multivariate analysis showed that p53 was the best predictor of survival independent of sex, age or prior treatment. Following 5-FU hepatic arterial infusion, patients with a high TS expression had a shorter survival time than those with a low expression (P = 0.025). The anti-apoptotic protein mcl-1 was the only factor, which correlated with response to 5-FU treatment. Thirty-five percent of patients with a diffuse mcl-1 expression responded whereas ninety percent of patients with a peri-nuclear expression responded (P = 0.041). Conclusions: These results indicate that besides TS, also Rb, p53 and mcl-1 are correlated with clinical outcome in patients with liver metastases from colorectal cancer.