Tumor DNA content was determined by flow cytometry in 24 surgically resected specimens from patients with primary lung cancer to compare results from fresh and paraffin-embedded specimens. We found a good correlation in DNA indices between fresh and paraffin-embedded specimens (r = .978), although one tumor with DNA near-diploidy was mistaken as DNA diploid in paraffin-embedded specimens. In the measurements of paraffin-embedded specimens, eight of 24 tumors were DNA multiploid and showed DNA content heterogeneity. These results indicate that DNA content analysis of paraffin-embedded specimens is helpful because it makes it easy to analyze multiple specimens from different parts of the tumor.