Gallium-67 scintigraphy was performed on 87 patients with a variety of histological types of untreated primary lung carcinoma. Gallium-67 uptake was determined, allowing for differences in tumor size. Differential uptakes were found for the various tumor types, with anaplastic small-cell carcinoma having the greatest average uptake, and adenocarcinoma and anaplastic large-cell carcinoma the smallest. Gallium-67 uptake was compared with response to radiation therapy, incidence of metastasis, and host survival in 58 of the patients. From these results it is suggested that the greater the Ga-67 accumulation in the tumor, the more effective is radiation therapy in reducing tumor size. Gallium-67 scintigraphy appears to be a valuable tool in estimating the sensitivity of the tumor before radiation therapy and in indicating the prognosis following radiation therapy in patients with primary lung carcinoma.