Within oligonucleotides 2-azapurine and especially 2-azaadenine bases form specifically base pairs with guanine. This base pair is of analogous stability as an adenine-thymine but less stable than a guanine-cytosine base pair. Therefore, the incorporation of 2-azaadenine residues into oligonucleotides instead of cytosine leads specifically to hybridization complexes with nucleic acids with homogenous stability. This is useful for the adaptation of the stabilities of different oligonucleotide sequences in all kinds of hybridization techniques, for example in oligomer chip technology.