This is the first report of an on-going Phase III protocol for patients with locally-advanced, non-metastatic, measurable lung cancer. The study randomizes two arms: 6000 rad using 500 rad fractions once a week (1 X W) for 12 weeks with spinal cord (SC) protection at 3000 rad; and 6000 rad using 200 rad fractions daily (5 X W) for 6 weeks with SC protection at 4500 rad. Both arms use an initially large loco-regional field that is further reduced when tumor doses reach 3000 rad in (1 X W) arm and 5000 rad in (5 X W) arm. The protocol was activated April 1982; as of August 1984, it had accrued 100 patients of whom 68 were evaluable [29 (1 X W) and 39 (5 X W)]. There have been no major differences in tumor responses or failure patterns between the (1 X W) and (5 X W) arms; response rates have been 69 and 64%; CR 31 and 20%; total incidence of local failures 20 and 23%; and overall incidence of distant failures 34 and 43%, respectively. The (1 X W) arm has been far better tolerated with 76% of its patients free of any esophagitis and 97% without weight loss, as compared to only 33 and 67% in the (5 X W), respectively. The (1 X W) arm has not conveyed loss in tumor control effectiveness, in-treatment progression, or higher incidence of distant spread. Subacute and chronic complications have been minimal with either treatment. No fatal or life-threatening toxicities have occurred; the incidence of severe complications has been 7% in the (1 X W) arm and 8% in the (5 X W) arm. Nevertheless, the number of patients alive and at risk greater than or equal to 12 months is still relatively small; definitive statements regarding very late toxic reactions cannot yet be made. Compared to their protocyptes [a (1 X W) Pilot Study and the 6000 rad/6 weeks arm of RTOG Protocol 73-01], results in the present protocol arms have not been different from what was expected. Once a week RT yields results that appear no different from those achieved with conventional RT in lung cancer.