The value of blood tests as prognostic factors in patients with recurrent rectal carcinomas treated with radiotherapy was studied in one retrospective (n = 114, 1976-1984) and one prospective (n = 100, 1985-1989) group of patients. The retrospective group was used for validation of the results from the prospective group. In univariate survival analyses, 19 of totally 38 variables significantly correlated to the survival. Of 13 significant blood parameters, lactate dehydrogenase (LD), erythrocyte sedimentation rate (ESR), alpha 1-, alpha 2-globulin, fibrinogen, carcinoembryonic antigen (CEA), C-reactive protein (CRP), haptoglobin, granulocytosis and thrombocytosis were the most important ones (p < or = 0.01). In the multivariate analyses (Cox regression) of the prospective group, LD, alpha 1-globulin, diagnosed liver metastases and CEA were found to be significant predictors of survival. A prognostic index was derived from the prospective group including ESR, LD and relapse-free interval. This clearly separated the patients in the retrospective group into one low- and one high-risk group.