Among the different investigated biomarkers, cell proliferation has provided valuable information on the clinical outcome of patients with malignant tumors. In the present study, we analyzed the potential relevance of fractional incorporation (FI) of a nucleotide precursor (3H-thymidine, 3H-dT) into DNA of tumor cells, determined on the primary tumor, on long-term clinical outcome of a series of patients with colorectal cancer. Determination of 3H-dT FI was carried out on fresh tumor material obtained at surgery as part of the clinical management of the primary tumor in 28 patients with colorectal cancer. Analysis of the relation between the FI and clinico-pathological characteristics of the tumor showed a trend of an inverse relation between the biomarker and Dukes' stage and no relation with tumor site. At 6 year follow-up, alive patients had a statistically significant higher median FI value (2.4%; range: 1.1-6.5%) than dead patients (1%; range: 0.3-4.5%) (p=0.02). Owing to the simplicity of this inexpensive methodology, the preliminary results of our study would indicate the potential of FI, a metabolic-kinetic parameter, to give prognostic information in colorectal cancer patients.