From Dec. 1990 to Aug. 1991, 109 patients with NSCLC were randomized into two groups. The first was treated by hyperfractionated irradiation (HF) with 1.15-1.25Gy per fraction, twice daily (interval > or = 6 hrs between fractions), and total doses of 69.6 +/- 2.1Gy. The other was conventional irradiation (CF) with 1.8-2.0Gy per fraction, once a day, and total doses of 63.9 +/- 1.1Gy. All but 11 was included in the analysis. The results showed that HF, compared to CF, could improve immediate response rates in patients with squamous cell carcinoma or with tumor size of 3-6cm (P < 0.05). The comparison of 1 and 2 year survivals did not show significant difference, but 1 year local control rate was 47.3% in HF and 29.1% in CF, P < 0.05. Further stratified analysis showed that the 1 and 2 year local control rates in patients of HF in stage I-IIIa were 54%, 28%; 39%, 13% in patients of CF in stage I-IIIa, P < 0.05. The 1 and 2 year survival rates in patients in stage I-IIIa were 64%, 32% in HF; 18%, 6% in CF, (P < 0.05). An assessment of acute and late toxicity showed no significant difference in incidences between the two groups. It is concluded that HF, compared to CF, can improve 1 and 2 year survival and local control rates of patients in stage I-IIIa.