Ornithine decarboxylase (ODC) is a key enzyme in the biosynthesis of polyamines, which are essential for cell proliferation. ODC activity was measured in 47 colorectal cancer patients, 5 patients with adenoma of colorectum and 4 healthy volunteers. Mean ODC activities of cancer tissue, non-cancerous mucosa from cancer-bearing colorectum, adenoma tissue, and normal mucosa from healthy volunteers were 435+/-392, 154+/-173, 295+/-202, 103+/-60 pmol CO2/h/mg protein, respectively. ODC activity of cancer tissue or adenoma tissue was significantly higher than that of the others. Among colorectal cancer patients, ODC activity in cancer tissue was correlated with T factors, lymph node metastasis and stages. Patients with tumors that had high ODC activity (> or =350 pmol CO2/h/mg protein) showed a poor 10-year survival rate. These results suggest that ODC activity may be a useful marker for patients' prognosis after surgery.