Forty-nine patients with very advanced locoregional lung cancer, metastatic in 41% of the instances, were treated with 5 Gy once weekly to a total dose of 50 to 60 Gy (1826-2050 ret). The overall tumor response rate was 68% (27% complete response and 41% partial response). The largest number of responders and the majority of complete responses were seen with the higher doses (60 Gy). The response rates of the major histologic variants were 100%, 75%, and 47% for small cell, large cell, squamous, and adenocarcinomas. The time to achieve more than 50% reduction in tumor size was 2, 2, 6, and 9 weeks for these histologic variants, respectively. The overall incidence of local failures was 22%, with only 10% of the patients demonstrating exclusive in-field local failures. There are 13 long-term survivors and the main cause of patient deaths was metastatic disease. The technique was extremely well tolerated, and, in fact, practically no acute radiation-induced complications were observed during the 10 to 12 weeks' treatment duration. Only one patient developed a symptomatic but transient radiation pneumonitis. Radiation fibrosis of various degrees has occurred, but it has been mostly asymptomatic and analogous to what is normally seen using conventional continuous schedules delivering similar doses. Once-a-week irradiation emerges as a practical and convenient alternative for the treatment of lung cancer, and appears to achieve similar results to conventional continuous schedules.