Several investigators have reported that alterations of the multiple tumor suppressor 1 (MTS1) gene frequently occurred in certain types of tumors. We examined the expression levels and somatic mutations of the MTS1 gene in primary colorectal carcinomas. The MTS1 transcript was quantitatively detected in 14 of 17 tumors, but in only one case of adjacent normal mucosa. Direct sequencing of the amplified MTS1 gene showed no somatic mutation in 17 primary colorectal carcinomas. These results indicate that inactivation of the MTS1 gene is not involved in pathogenesis of primary colorectal carcinomas, and that its enhanced expression is, instead, associated with primary colorectal carcinomas, especially markedly in the early stage of tumor progression.