Expression of the apoptosis-promoting Fas gene is frequently reduced or lost during the development of colorectal carcinoma. However, loss of heterozygosity at the Fas locus or Fas gene rearrangements do not account for the loss of expression of Fas, raising the possibility that methylation of the Fas promoter may inhibit gene expression in colorectal carcinomas. We have examined the Fas promoter region CpG island for evidence of hypermethylation in colorectal tumours. Forty-seven specimens of colorectal adenoma and carcinoma, as well as six samples of normal colonic mucosa, were examined by Southern blotting for methylation at HpaII and Cfol sites in this region. No methylation was detected in any of the specimens, suggesting that hypermethylation is not primarily responsible for the loss of expression of the Fas gene during colorectal tumorigenesis.