We describe a case of partial regression of metastatic hepatocellular carcinoma after treatment with thymostimulin. The patient, a 58-year-old man, received no specific therapy for his tumor, but only a thymus extract ("thymostimulin"). At follow-up 6 months later the patient showed clinical improvement, reduction of alpha-fetoprotein level an liver lesions, and a complete regression of lung metastases. The patient died of progression of the disease with 2-year overall survival.