The search for mRNAs that are specifically expressed in cancer tissues is important for gene diagnosis and therapy. However, finding such mRNAs in human cancers is usually very difficult, both because of the limited volume of RNA obtainable from the tissues and the many technical difficulties of RNA analysis. To address these problems, the present study compared mRNA from thyroid cancer tissues with those from normal and benign tissues by reverse transcription-PCR using two degenerate primers. Amplified cDNAs were separated by electrophoresis with nondenaturing acrylamide gel, then three bands that are increased in cancer tissues were selected, reamplified by PCR, and cloned into T-vector. One of the bands was determined by sequencing analysis to be oncofetal fibronectin. The expression of oncofetal fibronectin mRNA in benign and malignant tissues was examined by Northern blot and reverse transcription-PCR using specific primers of its cDNA sequence, and its increased expression was observed only in papillary and anaplastic carcinomas. Thus, the present method rapidly detected specific mRNAs in cancer tissues, and one of these, oncofetal fibronectin mRNA, is a good target for gene diagnosis of papillary carcinoma.