A chemistry was developed that permits on DNA-arrays both the covalent immobilisation of pre-fabricated nucleic acids-such as oligonucleotides, PCR-products or peptide nucleic acid oligomers-and the in situ synthesis of such compounds on either glass or polypropylene surfaces. Bonding was found to be stable even after some 30 cycles of stripping. Due to a dendrimeric structure of the linker molecule, the loading can be modified in a controlled manner and increased beyond the capacity of glass without negative effects on hybridisation efficiency. Also, the chemistry warrants the modulation of other surface properties such as charge or hydrophobicity. Preferentially, attachment of nucleic acids takes place only via the terminal amino-group of amino-modified oligonucleotides or the terminal hydroxyl-group of unmodified molecules so that the entire molecule is accessible to probe hybridisation. This derivatisation represents a support chemistry versatile enough to serve nearly all current forms of DNA-arrays or microchips.