Techniques for preparing catalytically active corrin complexes of cobalt with monofunctional e-carboxyl- and e-amino groups in a macroligand are suggested. Two methods of the covalent attachment of such Co-corrin complexes to the terminal 3'- and 5'-phosphate groups of oligodeoxyribonucleotides were studied: the introduction of the complex to the oligonucleotide after oligonucleotide synthesis in aqueous solution and in the course of automated solid-phase oligonucleotide synthesis. Introducing of the Co-corrin complex during solid-phase synthesis was more efficient. It was demonstrated that the oligonucleotide probe thus obtained was able to act as a nuclease in the presence of ascorbic acid, the location of the clearage sites being determined by the addressing oligonucleotide.