Lysyl oxidase (LOX) is an extracellular amine oxidase catalyzing formation of lysine-derived cross-linkages in collagen and elastin in extracellular matrices. Four human paralogs of LOX (LOXL1, LOXL2, LOXL3, and LOXL4) have been identified, each encoding the functional domains required for the amine oxidase activity of LOX. Upregulated expression of LOX and LOXL2 was reported to show significant correlation with absence of lymphovascular invasion in tumor tissues from patients with colorectal adenocarcinoma, suggesting that oxygen tension around tumors may be an important factor in expressional regulation of these genes in colorectal carcinomas. To evaluate the effects of hypoxia on expression of LOX and LOXL2 in colorectal carcinomas, we performed promoter assays and RT-PCR analysis under hypoxia in colorectal carcinoma cell lines, HT-29 and HCT-116. Expression of LOX was upregulated under hypoxia in both HT-29 and HCT-116 cells, whereas LOXL2 expression was not affected by hypoxia in those cells. In the highly metastatic HCT-116 cells, LOX showed a higher level of upregulation than in HT-29 cells, suggesting a possible association of LOX upregulation with increased invasiveness and metastatic potential in colorectal carcinomas.