During colorectal cancer (CRC) development, in addition to genetic alterations, several epigenetic changes, including DNA methylation in the promoter regions accumulate in tumor cells. Cell-free DNA (cfDNA) in the circulatory system can originate also from tumor tissue; therefore the evaluation of methylated cfDNA in the plasma can be a promising method for early cancer screening. In my Ph.D., I have investigated the rate of cfDNA's release and stability using animal models. I aimed to compile an epigenetic marker panel, which contains genes with altered DNA methylation patterns in the healthy-colorectal adenoma-cancer sequence. I have found that the methylation level of SFRP1, SFRP2, SDC2, and PRIMA1 gene promoters has already increased in adenoma stages in both tissue and plasma samples. Immunohistochemistry analyses indicated decreasing protein expression in parallel with elevated methylation. According to our results, cfDNA amount and the methylation have been influenced by DNA isolation and blood collection methods.