The results of serum gamma-GT activities of 36 laryngeal cancer patients, were compared with that of 40 patients of benign group and 61 normal persons of control group, the difference between the first group and the other two groups is statistically significant (P < 0.01), whereas the difference between the later two groups shows no significance (P > 0.05), so measuring the serum gamma-GT activity is a simple and useful method for laryngeal cancer diagnosis. By following up 9 laryngeal cancer patients, the results indicated that measuring serum gamma-GT activity at regular intervals after treatment is a simple and useful method for observing the therapeutic effect, and for monitoring tumor recurrence or metastases.