Pt(2+)-containing derivatives of oligodeoxyribonucleotides were used to evaluate the ligand affinity to the template sites of Klenow fragment of DNA polymerase I from E. coli and DNA polymerase alpha from human placenta. The values of Kd and Gibb's energy (delta G degree) for the complexes of oligodeoxyribonucleotides and their derivatives with the template sites of these enzymes were determined from the effects protecting the enzyme from inactivation by Pt(2+)-containing oligonucleotides. Kd and delta G degree values of the complexes made by DNA polymerases and orthophosphate, triethylphosphate, d(pC)n, d(pT)n, d(pG)n, d(pA)n (where n = 1-25), heterooligonucleotides of various length and structure, and oligothymidylates with partially and completely ethylated internucleotide phosphates were evaluated. The obtained data enabled us to suggest 19-20 mononucleotide units of the template to interact with the protein. Only one template internucleotide phosphate forms a Me(2+)-dependent electrostatic contact (delta G = -1.1...-1.7 kcal/mol) and a hydrogen bond (delta G = -4.4...-4.9 kcal/mol) with the enzyme. It is likely that the mononucleoside units of the template form hydrophobic contacts with the enzymes. The efficiency of such interaction changes with the hydrophobicity of the bases: C less than T less than G approximately A. For both homo- and heterooligonucleotides the contributions of nucleoside units to the affinity of the templates to the enzymes is due to the complementary interactions with the primers. A hypothetical model for the template-primer interaction with DNA polymerases is suggested.