As a result of thermolysin hydrolysis of a coat protein (CP) of Potato Virus M Ukrainian Strain VI (PVM), the heptapeptide ²⁹AADFEGK³⁵ was found to be recognised by two PVM specific monoclonal antibodies (MAbs) M6D5 and M9G1. This heptapeptide represents the C-terminal part of tryptic tetradecapeptide ²²EARPLPTAADFEGK³⁵ (P14) which was also recognised by the same MAbs. The peptides represented sequences of tryptic (P14), thermolysinic (P7) fragments and three heptapeptides containing alanine substitutions for Asp³¹ and Glu³³, were synthesised to determine the contribution of dicarbonic amino acids in the antigen-antibody interaction. All synthetic heptapeptides were recognised by both MAbs weakly in indirect ELISA. These peptides were also used as inhibitors of MAb-CP and MAb-P14 reactions in inhibition ELISA. The results of inhibition ELISA have shown the following: 1) the same concentrations of peptides were more effective to inhibit the interaction of MAbs with P14 than with CP; 2) substitutions of charged amino acids decreased noticeably the ability of peptides to inhibit the antigen-antibody interaction, especially the substitution of Asp³¹ ; 3) heptapeptides containing alanine substitutions suppressed more effectively the interaction of MAb M6D5 with antigens and were less effective to inhibit the reaction of MAb M9G1 with the same antigens. Thus, the difference in Asp³¹ and Glu³³ contributions to the antigen-antibody complex formation has been found.