The Marfan syndrome is an autosomal dominant connective tissue disorder with pleiotropic manifestations affecting skeletal, ocular and cardiovascular systems. Because the fibrillar collagens are major structural components of connective tissue, the hypothesis has long been set forth that the Marfan syndrome is a disorder of fibrillar collagen. We have investigated this hypothesis by performing linkage studies in 12 multiplex families with the Marfan syndrome, using restriction fragment length polymorphisms (RFLP's) associated with 3 genes encoding chains of fibrillar collagens. The data exclude linkage to all 3 candidate genes in 2 families and at least 1 of the candidates is excluded in 6 additional families. Each candidate was excluded in at least 3 families. In no case was strong evidence in favor of linkage of the Marfan syndrome to any of the 3 genes observed. These data speak against the hypothesis that mutations in one or more of these 3 fibrillar collagens cause the classic Marfan syndrome.