Differentiation of the papillary variant of papillary thyroid carcinoma (PTC) from papillary hyperplasia in nodular goiter may be difficult in fine-needle aspiration biopsy (FNAB) by means of morphology alone. To improve cytodiagnostic accuracy the occurrence of MAGE-1, GAGE-1/-2 gene expression was analyzed by means of RT-PCR. The genes investigated are recognized by autologous T lymphocytes and are expressed in carcinomas of various sites e.g. lung, ovary, colon but not in non-neoplastic tissue except testis. Routinely obtained smears with cytologic diagnosis of PTC confirmed by histology (n=20) and diagnosis of nodular goiter (n=10) were investigated. The MAGE-1, GAGE-1/-2 PCR products were found in 6/20 of the carcinomas but in none of the benign lesions. To identify PCR products automatic gene-sequencing in all positive cases was performed. The data indicate that MAGE-1, GAGE-1/-2 gene expression may give additional information to delineate PTC from papillary hyperplasia in FNAB.