White Carneau pigeons(WCP)have previously been sbown to be genetically susceptible to the development of spontaneous atherogenesis. Analysis of levels of total hydroxyproline and isodesmosine in the thoracic aorta and celiac bifurcation of prelesion,six-week-old WCP and Show Racer pigeones (SRP), revealed an increased accumulation of total collagen and cross-liked elastin in the WCP arterial tissue. Using dot blot hybridization, measurements of steady state levels of several mRNA in total RNA extracted from pigeon aortic tissue were determined.While the increased deposition of extracellular matrix proteins was paralleled by significantly greater recovery of mRNA coding for pro α1(1) collagen and elastin, in RNA extracted from WCP aortic tissue, increased recovery of mRNA coding for an intracellular protem, γ-actin were observed in WCP aortic tissue.No differences in steady state levels of mRNA coding for pro α1(1) collagen and elastin were observed in RNA extracted from liver of WCP and SRP.The experiment results indicate that the cell population in WCP aortic tissue exhibits a markedly different phenotype with respect to a capacity for the biosynthesis of extracellular and intracellular proteins.