Chemotherapy of lung cancer has, until now, been an experimental approach that requires careful evaluation of tumor response. The growing number of lung cancer patients now undergoing chemotherapy has led to a rapid increase in the number of computed tomography (CT) scans performed. Eighty consecutive lung cancer patients (55 non-small cell and 25 small cell lung cancers) were included in a prospective study to analyze whether the standard chest roentgenography is as effective as computed tomography in evaluating tumor response. Both standard chest roentgenography and CT scanning were performed before the chemotherapy began and were repeated after 10 to 12 wk of treatment. Response evaluations were performed according to the World Health Organization recommendations. When two-dimensional measurements were possible, the indicator lesions were defined as measurable tumors. Both roentgenography methods were used, independently, to classify the response into the following categories: complete response, partial response, minor response, stable disease, and progressive disease. A comparison of CT scans versus standard chest roentgenography as a measurement of indicator lesion showed a concordance of borderline significance (kappa = 0.146, p less than 0.05); a significant asymmetry was demonstrated (McNemar = 35.6, p less than 0.001), indicating that CT scanning may be a more appropriate method for measuring tumors than standard chest roentgenography. Moreover, no concordance was observed comparing CT scan and standard chest roentgenography measurability in the subgroups of patients with T3 or T4 tumor, hilar tumor, and patients with pleural effusion or atelectasis in which the McNemar test of symmetry constantly showed a better measurability using CT scan.(ABSTRACT TRUNCATED AT 250 WORDS)