PURPOSE: To evaluate the significance of serum SCC for the monitoring of treatment response and the early detection of distant metastasis during radiotherapy (RT). MATERIALS AND METHODS: In 13 patients with histologically proven primary squamous cell carcinoma of uterine cervix, serum SCC values were checked in pre-RT point, weekly during RT, and in post-RT point. RESULTS: In 4 of 13 cases, metastasis appeared at the end of external RT, so that intracavitary radiation couldn't be performed. Of these 4 cases, 3 with elevated pre-RT SCC level, who resulted in lung metastasis on chest PA at the end of external RT showed decreased post-RT SCC value despite of metastasis. Of all 10 cases with elevated pre-RT SCC value (including 3 with metastasis at the end of external RT), SCC value was higher than pre-RT value in 7 at 9 Gy and the difference was statistically significant. At 18 Gy, SCC was higher in 4 and lower in 6 than pre-RT value. After 18 Gy, SCC value decreased continuously to the end of RT in all 10 cases. CONCLUSION: During RT, SCC value increased initially at 9 Gy. To 18 Gy, SCC value decreased to the nearly same with pre-RT value. After 18 Gy, to the end of RT, SCC value decreased continuously and normalized in completely responded cases. In cases with appearance of lung metastasis, SCC value also decreased with the disappearance of main mass of uterine cervix despite of metastasis.