The role of fibrillin-1 in metanephrogenesis was investigated. Fibrillin-1 cDNA was isolated from the rat kidney cDNA library and sequenced, and its spatiotemporal expression was studied. It had ∼88% homology with human fibrillin-1 and had Ca²⁺binding epidermal growth factor-like domains, transforming growth factor-β binding protein motifs, and an RGD binding site. Northern blot analysis revealed an ∼10-kb transcript, and fibrillin-1 expression was developmentally regulated. In situ hybridization and immunofluorescence studies indicated that at day 15 of gestation, fibrillin-1 is expressed in the metanephric mesenchyme. At day 18, its expression was confined to nascent blood vessels and glomeruli, and it increased in the newborn and neonatal kidneys. Immunoprecipitation revealed an ∼300-kDa band by SDS-PAGE. Treatment with fibrillin-1 antisense oligodeoxynucleotide induced marked dysmorphogenesis of the embryonic metanephroi. Concomitantly, the fibrillin-1 mRNA, antibody reactivity in the metanephroi, and fibrillin-1-specific radioincorporation were reduced. These data indicate that, like α_vβ₃integrin, a known morphogen and a putative receptor of fibrillin-1, the fibrillin-1 modulates events related to early organogenesis and possibly also the vascularization of the rat kidney.