The relations between patient characteristics and prognosis were examined in 340 patients with advanced colorectal cancer treated with chemotherapy. Variables were tested for relation to survival and responses in univariate and multivariate analyses. Performance status (P less than 0.001), number of symptoms (P less than 0.001) and haemoglobin level (P less than 0.001) were the most important variables for survival in univariate analyses. In the multivariate analyses of survival, haemoglobin level (P less than 0.001) and disease-free interval (P less than 0.01) were the most influential variables. In addition, number of symptoms (P less than 0.01), performance status (P less than 0.05) and treatment of the primary tumour (P less than 0.05) were independently related to survival. The main independent determinant of response was haemoglobin level (P less than 0.01). Besides these pretreatment characteristics, type of chemotherapy regimen influenced both response rate and survival in multivariate analyses (P less than 0.001). We conclude that haemoglobin level, disease-free interval, symptoms and performance status are important prognostic factors in advanced colorectal cancer. The distribution of these variables may influence the results of clinical trials.