To understand the cellular origin and mechanism of gene expression in amylase-producing cancers, the phenotyping of amylase isogenes by the polymerase chain reaction and restriction-fragment-length polymorphism using restriction endonucleases TaqI, DdeI, HinfI, and AfaI were performed for 3 amylase-producing lung adenocarcinomas, 16 lung cancers without hyperamylasemia, other human malignant neoplasms, cultured cell lines, and normal tissues. In addition, amylase mRNA transcripts were semi-quantified by the limited polymerase chain reaction. Amylase mRNA transcripts were detected in all of the tissues examined. The AMY1 gene (salivary type) was exclusively and highly expressed in the salivary glands and the amylase-producing lung adenocarcinomas. Coexpression of the AMY1 gene and AMY2 gene (pancreatic type) was observed in most of the lung cancers without hyperamylasemia, lung tissue, and cells scraped from the tracheal epithelium, thyroid, and female genital tract (ovary, fallopian tube, and uterus cervix), while minimal levels of mRNA transcripts of the AMY2 gene were detected in other malignant neoplasms, various normal tissues, and the cultured cell lines. All mRNA transcripts identified as being those of the AMY2 gene were further identified as being from the AMY2B gene except for the transcripts from the pancreas, in which the AMY2A gene and AMY2B gene were coexpressed. On the basis of these results, the clinical occurrence of amylase-producing cancer likely relates to the tissues expressing the AMY1 gene, while the AMY2B gene, which evolutionarily is the oldest gene among human amylase isogenes, is constitutively expressed in various tissues.