The methods of flow birefringence, low shear viscometry, and circular dichroism were used to investigate the DNA conformation in solution during the interaction with coordination compounds [Co(NH₃)₆]Cl₃ and [Co(NO₂)₆]Na₃. It has been shown that the compound [Co(NO₂)₆]Na₃, which dissociates in an aqueous solution to produce a negative complex ion [Co(NO₂)₆]^3-, binds to a DNA molecule, causing considerable changes in its parameters. For the binding to occur, the complex ion must undergo a transition to its aqueous form. Even a low cobalt content is shown to produce DNA shrinkage. It is attended by an increased DNA optical anisotropy. This effect was observed for both compounds used. The comparison of these data with earlier results on DNA-Fe³⁺ interaction has revealed some features common to the DNA binding to trivalent metal ions. We have suggested that the mutual orientation of DNA statistical segments is changed because of the formation of intramolecular linkages between trivalent ions and remote DNA chain segments.