Oncogene amplification is frequent in many epithelial tumors and often associated with advanced tumor progression. In different epithelial neoplasias it helps to provide prognostic information on individual patients. The present study was performed to evaluate the hitherto unknown prevalence of INT-2 gene amplification and its potential usefulness as prognostic marker in patients with human thyroid cancer. We used differential quantitative polymerase chain reaction and fluorescent DNA technique as a reliable method to detect low copy-number amplification of oncogenes from archival carcinoma specimens. Sequences from the int-2 gene and the single copy gamma-interferon gene were amplified simultaneously by PCR and quantified on a fluorescence activated sequencer. Native tumor tissue from 63 patients with differentiated thyroid cancer (43 papillary, 3 oncocytary, and 17 follicular) and from 12 goiters was analyzed by differential quantitative polymerase chain reaction. The study group contained many far advanced tumors. 40% of tumors were recurrent, 35% were staged T4 tumors and 70% presented with lymph node metastases. The prevalence of INT-2 amplification was 12% for follicular and 7% for papillary carcinomas. In goiter tissue no amplification was found. Amplification was only 2-4fold in positive cases. Low grade amplification is of no apparent importance in differentiated thyroid cancer.