Several minor modifications of the presented method may be considered to improve the accuracy of Kd determination via ELISA. Limitation of non-specific interaction between phage particles and plate/surface-immobilized proteins and revision of phage concentration measurement would be the most significant improvements. However, the proposed mathematical interpretation of interactions between polyvalent receptors sheds new light on the field of affinity determination in phage-peptide systems, similar to the theory presented by the previous authors . The presented model was compared with empirical results that confirm the hypothesis about the mixed valency of phage particles depending on the number of pIII. Studies on peptide-protein complex formation and dissociation in other experimental systems may be discussed in a separate paper to provide comprehensiveness of the field of Kd determination in biochemical sciences. Invitrogen/Thermo Fischer Scientific (USA). Isolation of phage DNA was performed as stated in , and sequencing of the phage genome was performed by Genomed (Poland) using -96pIII primer (NEB). Horseradish peroxidase-conjugated anti-M13pVIII monoclonal antibody was bought from Lab-Jot (NEB, USA) and used in dilution 1:5000, while 3,3',5,5'tetramethylbenzidine (TMB, HRP enzyme substrate) was delivered by Thermo Fisher Scientific (USA) and used without pretreatment.