Heparin-binding peptides are provided of the formula R.sub.1(X.sub.1B.sub.1B.sub.2X.sub.2B.sub.3X.sub.3Y.sub.1R.sub.2)R.sub.nR- .sub.3, R.sub.1(X.sub.1B.sub.1B.sub.2B.sub.3X.sub.2X.sub.3B.sub.4X.sub.4Y.- sub.1R.sub.2)R.sub.nR.sub.3, and C(X.sub.1B.sub.1B.sub.2B.sub.3X.sub.2X.sub.3B.sub.4X.sub.4).sub.nC; wherein X.sub.1, X.sub.2, X.sub.3, and X.sub.4 are independently selected from the group consisting of hydropathic amino acids; B.sub.1, B.sub.2, B.sub.3, and B.sub.4 are independently selected from the group consisting of basic amino acids; C is cysteine; Y.sub.1 is zero or one to ten amino acid residues, wherein at least one amino acid residue is proline; n is an integer from one to ten; and R.sub.1, R.sub.2, and R.sub.3 are independently selected segments containing from zero to twenty amino acid residues, provided, at least one of the segments R.sub.1, R.sub.2, and R.sub.3 comprises at least one hydrophobic amino acid residue. The peptide C(X.sub.1B.sub.1B.sub.2B.sub.3X.sub.2X.sub.3B.sub.4X.sub.4).sub.n- C is optionally cyclized via a disulfide bond formed between cysteine residues. The peptides are administered to reduce plasma LMWH and heparin levels and to reduce the anticoagulant effects of heparin and LMWH. The peptides are also administered to inhibit microbial growth and to inhibit mast cell serine proteases involved in various diseases and disorders. The peptides are also administered as carriers to deliver active agents.