Abstract The major histocompatibility complex (MHC) in the chicken (B-complex) encodes glycoproteins homologous in function and distribution to the mammalian MHC. These are the B-F (class I) and B-L (class II) glycoproteins. In addition, a third glycoprotein (B-G) is also encoded by the chicken MHC. We are interested in examining gene regulation and cellular expression of these MHC gene products in the chicken. The trisomic line of chickens is being developed as an animal model for this purpose. Birds from this line contain either 2, 3, or 4 MHC-encoding chromosomes. In this study, we investigated the hypothesis that the quantities of B-complex glycoproteins on the membranes of fully differentiated erythrocytes are proportional to the number of MHC-encoding chromosomes present in particular birds. Hemagglutination final titer and quantitative adsorption assays were carried out using erythrocytes from disomic and aneuploid chickens homozygous for the B 15 haplotype. The average hemagglutination final titers were higher for tetrasomic cells as compared to disomic cells. Furthermore, in adsorption assays, employing a B15 cross-reacting alloantiserum, trisomic and tetrasomic erythrocytes displayed increased adsorption capabilities (1.6 and 3.1 fold, respectively) compared to disomic control cells. These results indicate a step-wise increase in the amounts of erythrocyte surface glycoproteins per cell in the trisomics and tetrasomics, respectively. Such findings are consistent with a MHC-dosage-dependent model of gene expression in homeothermic vertebrates.