Flow cytometrically determined nuclear DNA content has been measured on 74 formalin-fixed, paraffin embedded specimens of non-small cell carcinoma of the lung. Of the 60 tumors that were successfully analyzed, 32 (53%) were diploid and 28 (47%) were aneuploid. The mean DNA index of aneuploid tumor was 1.5 +/- 0.25, ranging from 1.1 to 2.0. There was no significant correlation between DNA ploidy and the patient's clinical characteristics, histology of tumor, nodal status or tumor stage. Tumor ploidy was not found as a prognostic determinant in non-small cell carcinoma of the lung in this study.