In an attempt to isolate potential molecular targets for diagnosis, treatment and/or prevention of colorectal cancer (CRC), we have been analyzing expression profiles of clinical samples from CRC patients using genome-wide cDNA microarray. Among the genes up-regulated frequently in colorectal tumors, we here focused on TOMM34 (34 kDa-translocase of the outer mitochondrial membrane). Immunohistochemical staining revealed significant accumulation of TOMM34 protein in CRC tissues compared with their corresponding non-cancerous mucosae. Transfection of colon cancer HCT116 cells with short-interfering RNA (siRNA) specific to TOMM34 effectively suppressed its expression and drastically inhibited cell growth. These findings suggest that TOMM34 is involved in the growth of cancer cells, and may contribute to the development of novel anticancer drugs and/or diagnosis for CRC.