The goal of the study was to investigate the relationship between the polymorphism of alpha-amylase and the erythrocyte systems--ABO, MNSs, and determine their population distribution and individual phenotype and gene incidence.Parallel examinations of identical blood samples were carried out to determine the phenotypes of alpha-amylase and ABO and MNSs blood group systems. Blood was obtained by venipuncture in the Serological Laboratory of the Department of Forensic Medicine at the Medical University of Plovdiv. Amylase phenotypes were determined by the authors' own modification of Kompf's method using continuous horizontal electrophoresis of blood serum on agarose gel. Only the classical phenotypes of the examined blood group systems--alpha-amylase, ABO and MNSs were determined in the study. RESULTS. The analysis of the data by chi-square analysis using Pearson criterion found no relationship between the polymorphism of the serum alpha-amylase and ABO and MNSs erythrocyte systems. The allele frequencies determined were 1(a) = 0.9595, 1(b) = 0.0388, 1(o) = 0.0017 for Amyl and 2(a) = 0.9579 and 2(b) = 0.0421 for Amy2.The difference between the observed and expected phenotypes of the examined blood group systems alpha-amylase, ABO, MNSs is short of statistical significance. This indicates genetic stability of the examined blood group systems in the studied population.