Compounds comprising peptides and peptidomimetics capable of binding the C3protein and inhibiting complement activation are disclosed. These compoundsdisplayimproved complement activation-inhibitory activity as compared with currentlyavailable compounds. Isolated nucleic molecules encoding the peptides are alsodisclosed. Also disclosed is a method for making the compounds and use of suchcompounds, such as artificial organ, artificial implant or tubing, coated withacompound of the invention that inhibits complement activation. A method formakingthe compounds is disclosed which includes synthesizing the peptide bycondensationof the amino acid residues or analogs thereof or comprising expressing apolynucleotide encoding the peptide or a concatemer of the peptide, which ispost-translationallycleaved to form the peptdide. Also disclosed are compoundscomprising a peptide having a sequence: Xaa1 - Xaa2 - Cys - Val - Xaa3 - Gln -Asp- Trp Gly - Xaa4 - His - Arg - Cys - Xaa5 - Xaa6 - Xaa7 (SEQ ID NO:15)；wherein:Xaa1 is missing or is Gly； Xaa2 is Ile, Val, Leu, Ac-lle, Ac-Val, Ac-Leu ortogetherwith Xaa1 is dipeptide Gly-lle； Xaa3 is Trp or an analog of Trp that comprisesasubstituted or unsubstituted bicyclic aromatic ring component or two or moresubstituted or unsubstituted monocyclic aromatic ring components； Xaa4 is His,Ala,Phe or Trp； Xaa5 is L-Thr, D-Thr, Ile, Val, Gly, or together with Xaa6 andXaa7 istripeptide Thr-Ala-Asn； Xaa6 is missing or is Ala； and Xaa7 is missing or isAsn.
