NOTCH proteins (NOTCH1, NOTCH2, NOTCH3 and NOTCH4) play crucial roles in embryonic development. Also, mounting evidence indicates that NOTCH contributes to the pathogenesis of hematopoietic and solid malignancies. Recent studies reported a high incidence of gain-of-function mutations of the NOTCH1 gene in T-cell acute lymphoblastic leukemias (ALL). To see whether NOTCH1 mutation occurs in other malignancies, we analyzed NOTCH1 for the detection of somatic mutations in 334 malignancies, including 48 lung, 48 breast, 48 colorectal and 48 gastric carcinomas, and 142 acute leukemias (105 acute myelogenous leukemias, 32 B-ALLs and 4 T-ALLs) by single-strand conformation polymorphism assay. Also, to see whether other NOTCH genes harbor somatic mutations, we analyzed NOTCH2, NOTCH3 and NOTCH4 genes in the same tissue samples. Overall, we detected three NOTCH mutations in the cancers, which consisted of one NOTCH1 mutation in the T-ALLs (25.0%), one NOTCH2 mutation in the breast carcinomas (2.1%), and one NOTCH3 mutation in the colorectal carcinomas (2.0%). There was no NOTCH mutation in other malignancies analyzed. Our data indicate that NOTCH1 is mutated in T-ALL, but not in other common human cancers, and that NOTCH2, NOTCH3 and NOTH4 genes are rarely mutated in common human cancers. Despite the importance of NOTCH activation in many types of human cancers, mutation of NOTCH genes, except for NOTCH1 mutation in T-ALL, may not play an important role in the tumorigenesis of common cancers.