To identify the transcription termination elements in the mouse gastrin gene, we examined RNA transcripts after stable transfection of gastrin expression plasmids into the NIH3T3 cell line. The GT-repeat region at the 3'-flanking sequence of the mouse gastrin gene acted as a transcription terminator. When the GT-repeat unit was deleted from its site, the effect of termination disappeared. Further experiment, using serial deletion mutants, revealed that the 56-38 nucleotide upstream region from the GT-repeat unit also participated in transcription termination. We propose that the upstream region of the GT-repeat unit might be recognized as a pause site by the RNA polymerase II, and an abnormal DNA structure, derived from the GT-repeat unit, might function as a blockage of polymerase processivity.