The Feulgen-DNA content of cell nuclei from the human larynx was assessed in 62 lesions from 14 patients with dysplastic and cancerous lesions and in 14 control patients with non-neoplastic chronic laryngitis. All the carcinomas displayed aneuploid cell nuclei, and the cellular DNA content was substantially altered in dysplasias which later progressed to cancer in situ or invasive cancer. Thus the process of laryngeal carcinogenesis can be monitored not only by histological changes, but also by cellular DNA aberrations. Quantitative DNA analysis appears to be a complement to the histopathological evaluation of laryngeal lesions in the search for neoplasia.