Using a PCR-amplified 5'-end proximal 600-bp fragment and two cDNA clones of cytosine DNA-methyltransferase gene of Arabidopsis thaliana as specific probes in hybridization with plant DNA samples, hydrolyzed by methylation-sensitive restriction endonucleases HpaII and MspI, it has been established that CCGG sites located in the 5'-end proximal part of cytosine DNA-methyltransferase gene are highly methylated at internal C and less but detectably methylated at external C residues. On the contrary, all CCGG sites in 3'-terminal half of the coding region were found to be unmethylated at both external and internal C residues. No significant differences between methylation patterns of cytosine DNA-methyltransferase gene in various organs (leaf, stem, flower) of the Arabidopsis thaliana plant were detected.