The DNA methylation status of the CpG islands within the 5′ flanking region of the CYP1B1 and CYP1A1 genes in seven colorectal cancer cell lines and 40 primary colorectal cancers showed CYP1B1 gene methylation in two cell lines (SW48 and Caco-2) and two (5%) cancers, but not in corresponding normal tissues. Here, CYP1A1 is linked to colorectal cancer.