Abstract: Fibrin-binding molecules are provided which include at least one peptide essentially corresponding to one or both of the following portions of the natural fibronectin molecule. The first portion is that portion which includes the .sup.4 F1..sup.5 F1 module pair of fibronectin and includes no more of the natural fibronectin molecule than the N-terminal 25.9 kDa proteolytic fragment. The second portion includes the .sup.10 F1..sup.11 F1 module pair of fibronectin and includes no more of the natural fibronectin molecule than the C-terminal 11 kDa proteolytic fragment. Also disclosed are nucleic acid molecules encoding the fibrin-binding peptides, methods for making the peptides, methods for using the peptides in the diagnosis and treatment of cardiovascular, peripheral vascular, cerebrovascular, and other conditions associated with fibrin deposition, and assay methods for detecting a fibrin-binding molecule and for measuring fibrin.