Phosphate-methylated dna shows a number of unique (bio)chemical properties. None of the other uncharged modified dnas possess these interaction qualities: a parallel right-handed duplex, an antiparallel left-handed duplex, selectivity for short fragments in succession hybridized with natural dna and the absence of hybridization with rna under physiological conditions.The significance of the chirality of phosphorus in duplex formation is discussed. Hybridization studies of phosphate-methylated rna compared to phosphate-methylated dna will be given. Moreover, the (bio)chemical properties of charged modified dnas will be discussed.