By using the predefined criteria (Muller et al, 2003), differential methylation was detected in APC, E-cadherin, hMLH1 and TIMP3. The frequency of detecting methylated DNA in the serum of cancer patients for APC was 17%, E-cadherin was 13%, hMLH1 was 41% and TIMP3 was 17%. The gene discussed is MLH1; the disease is cancer.