The primary structure of the 2265 residues of bovine plasma fibronectin has been completed. The new sequences reported in this paper are residues 600–868 (269 residues), 1138–1217 (80 residues), 1518–1599 (82 residues) and 1868–2061 (194 residues). These sequences constitute six type III homology units and two non-homologous connecting strands. Thus, there are fifteen type III homology units in plasma fibronectin. Evidence for two of the three splice variants found in rat liver cells [Schwarzbauer et al. (1983) Cell 35, 421–431] was obtained. No indication of the ‘extra’ type III domain present in some human fibroblast fibronectins [Kornblihtt et al. (1984) EMBO J. 3, 221–226] was found. Three carbohydrate groups (two glucosamine-based and one galactosamine-based) were identified, giving a total of eight carbohydrate groups in the longest splice variant of bovine plasma fibronectin. A second free sulfhydryl group (cysteine) was identified. This cysteine, like the first, is in a type III homology unit. HPLC patterns of peptides obtained from the C-terminal 6-kDa fragment suggested that the interchain bridge pattern of fibronectin is antiparallel. The bovine plasma fibronectin sequence is highly homologous to the human cellular fibronectin sequence deduced from the cDNA sequence [Kornblihtt et al. (1985) EMBO J. 4, 1755–1759].