Connective tissue composition of aortas from several non-human primate species has been studied in an effort to relate collagen, elastin, ang glycosaminoglycan (GAG) content to species susceptibility to atherosclerosis. Among the species studied the baboon contained the highest content of GAG in the aorta. While the distribution of individual GAG varied from species to species, heparan sulfate (HS) was the highest GAG in aortas from most of the species. The ratio of HS to chondroitin sulfates (CS) plus dermatan sulfate (DS) was lowest in the baboon, a species relatively less susceptible to atherosclerosis, and highest in the squirrel monkey, a very susceptible primate. If a relationship exists between HS to CS + DS ratio in the aorta and atherosclerosis, the primates can be arranged in the following decreasing order of susceptibility: squirrel, chimpanzee, stump-tailed, rhesus, African green, patas, baboon. In studies of other connective tissue components, the proportion of total collagen to elastin was found lowest in the baboon. Such observations emphasize the importance of connective tissue in the pathogenesis of atherosclerosis.