cDNA microarray analyses can be used to identify candidate genes that play important roles in human carcinogenesis. To gain insight into the molecular sketch of colorectal cancer, we have constructed cDNA microarrays specialized for colorectal cancer, which we named "Colonochip" by selecting genes that are expressed in colorectal cancer, normal colonic mucosa, and liver metastatic cancer tissues. This microarray contained 4608 nonredundant cDNA clones from over 30,000 cDNA clones derived from the three types of human cDNA libraries, as well as clones from 170 additional conventional major genes suspected to be involved in colorectal carcinogenesis, according to literatures. Using this "Colonochip," we were able to identify 59 genes showing twofold or more differential expression between primary cancer and normal colonic mucosa, potent candidates for diagnosis, and therapy of colorectal cancer for further studies.