We measured the maximum aggregation rate (MAR) of platelets in 770 patients with malignant head and neck tumors, 55 patients with benign tumors of the head and neck, and 164 healthy people as a control group. The results were as follows: 1. the mean MAR value of patients with malignant tumors was significantly higher than the control group mean value; 2. prior to treatment, the mean MAR value increased with advancing tumor stage; 3. both MAR values of relapsed or metastasized patients and of nonsurvivors in stage III and IV increased significantly compared with survivors or patients recovering from malignant tumors. The results of the present study suggest that MAR values of patients with malignant tumors of the head and neck may serve as indicators in evaluating therapeutic procedures and prognosis.