The TPR-MET oncogenic rearrangement was originally observed in an in vitro transformed human osteosarcoma cell line. Recently, we detected the expression of this rearrangement at very low levels in several cell lines derived from human tumors of nonhematopoietic origin using a highly sensitive method based on polymerase chain reaction amplification of the transcript. We report here the results of analysis of TPR-MET expression in cell lines derived from human gastric tumors and 22 biopsy samples of human gastric mucosa showing cancer or precursor lesions. The rearranged RNA was expressed in all four cell lines as well as in biopsy samples from 12 of the 22 patients. Overexpression of TPR-MET RNA in superficial gastritis lesions with hyperplasia of glandular neck cells suggests the possible involvement of this oncogene at an early stage of gastric tumorigenesis. Analysis of gastric biopsy samples for RAS gene mutations showed base substitutions occurring in the codon 12 region of Ki- and Ha-RAS genes in four cases, including two precursor lesions.