Our results indicated that in primary tumours, methylation of CpG sites in the proximal region of hMLH1 promoter is correlated with the loss of gene expression, while methylation is present in the distal region in all tissues tested, including normal mucosa and tumours which express hMLH1. The localization of methylation in hMLH1 promoter could help to analyse methylation status more accurately in samples from cancer patients. The gene discussed is MLH1; the disease is cancer.