Normal human laryngeal epithelia and laryngeal squamous cell carcinoma were assayed by Feulgen DNA cytofluorometry using free cell nuclei isolated from carnoy-fixed, paraffin-embedded specimens. In all of the 12 normal specimens, the epithelium showed typical diploid cell clones with low proliferative activity. Polyploid cells were seen in only two specimens from subjects aged 61 and 69 years respectively, and the number of polyploid cells seen in these two specimens was only two. Fifteen cancer cases were divided into three groups: an untreated group (5 cases), a chemotherapy group (5 cases) and a group of cases with recurrence after radiation therapy (5 cases). Among these three groups the DNA ploidy patterns were compared. In the untreated group, all cases showed a two-peak diploid pattern and a high proliferative activity, and polyploid cells were present. In the chemotherapy group, a wide one-peak histogram extending from 2C to about 5C was noted in 4 cases, and an aneuploid pattern in one case. Thus, the DNA ploidy pattern in the chemotherapy group differed from that in the untreated group. Of the 5 cases with recurrence after radiation therapy, one had a tetraploid pattern, but the remaining 4, a two-peak diploid pattern similar to that seen in the untreated group. Polyploid cells were observed in all these cancer cases. However, because they were also seen in some normal subjects, the finding of polyploid cells is not considered to be conclusive of cancer diagnosis.(ABSTRACT TRUNCATED AT 250 WORDS)