The interaction of calf thymus DNA (CT DNA) with trans-[PtCl ₂L ₂] and trans-[PdCl ₂L ₂] complexes (L–5-methyl-1H-tetrazol-1-ylacetic acid and its ethyl, butyl, and isobutyl esters; ethyl esters of 2-R-2H-tetrazol-5-ylacetic acids, R = Bu ^t, CH ₂CH ₂OH) have been quantitatively studied by a spectrophotometric method. The binding constants (K _b) of the tetrazolecontaining coordination compounds with CT DNA at pH 7.2 and 298 K are in the range of (3.67–5.93)•10 ⁵ mol L ^–1 for the Pd ^II complexes and (7.82–13.30)•10 ⁵ mol L ^–1 for and the Pt ^II complexes, respectively. The K _b values, as well as negative values of ΔG _b (–(31.7–34.9) kJ mol ^–1) indicate the effective binding between the studied complexes and CT DNA.