Tumor doubling times (DT) of 7 primary lung cancers and 3 metastatic pulmonary tumors were calculated with natural growth rates on plain chest X-ps. The median DTs of epidermoid carcinomas (n=5) , adenocarcinomas (n=2) and metastatic tumors (n=3) were 138 days, 343 days and 39 days, respectively. Predicted survival times (PST) were compared with actual survival times (AST) in each case. Three cases had survival benefits with cancer therepy.