To evaluate the effect of thymostimulin in a treatment schedule of concurrent hyperfractionated chemoradiation therapy, with the cytostatic forming part of each therapeutic fraction, the authors included in this protocol 36 patients with advanced head and neck carcinomas randomized into two groups. Group A received 115 cGy + 5 mg/m2 of carboplatin per fraction in two daily fractions for a total dose of 8.050 cGy + 700 mg of carboplatin, while group B received the same treatment associated with thymostimulin, with the following schedule: 1.5 mg/kg/day in the week before chemoradiation + 1.5 mg/kg twice a week during treatment + 1 mg/kg twice a week for two years or until recurrence. The results were evaluated upon reaching 18 months of follow-up (30 maximum). A smaller decrease in lymphocyte levels was observed in group B, but no differences were seen in toxicity between the groups. Patients included in the B group had a slightly longer disease-free-survival interval, but 17% of recurrences and 11% of distant metastases were observed in the A group, whereas 22% of recurrences and 22% of distant metastases were seen in the B group. The number of complete remissions (94%) was the same in both groups.