A compound that inhibits complement activation, which comprises a peptide having a sequence: Xaa1 Cys-Val-Xaa2-Gln-Asp-Trp-Gly-Xaa3-His-Arg-Cys-Xaa4 (SEQ ID NO: 15)； wherein: Xaa1 is Ile, Val, Leu, Ac-Ile, Ac-Val, Ac-Leu or a dipeptide comprising Gly-Ile； Xaa2 is Trp or an analog of Trp； Xaa3 is His, Ala, Phe or Trp； Xaa4 is Thr, Thr, Ile, Val, Gly, or a tripeptide comprising Thr-Ala-Asn, in which a carboxy terminal -OH of any of L-Thr, D-Thr, Ile, Val, Gly or Asn it is optionally substituted by NH2； and the two Cys residues are linked by a disulfide bridge, in which (a) the Trp analog in Xaa2 is a substituted or unsubstituted bicyclic aromatic ring or two or more substituted or unsubstituted monocyclic aromatic rings； or (b) the Trp analog in Xaa2 is selected from the group consisting of 2-naphthylalanine, 1-naphthylalanine, 2-indanylglycine carboxylic acid, dihydrotriptophan and benzoylphenylalanine； or (c) the Trp analog in Xaa2 is a substituted or unsubstituted indole, naphthyl or dibenzoyl； or (d) Xaa1 is Ac-Ile, Xaa2 is Trp or a Trp analog that is an indole, naphthyl or substituted or unsubstituted dibenzoyl, Xaa3 is Ala and Xaa4 is L-threonine or D-threonine.Un compuesto que inhibe la activación del complemento, que comprende un péptido que tiene una secuencia: Xaa1 Cys - Val - Xaa2 - Gln - Asp - Trp - Gly - Xaa3 - His - Arg - Cys - Xaa4 (SEC ID Nº:15)； en la que: Xaa1 es Ile, Val, Leu, Ac-Ile, Ac-Val, Ac-Leu o un dipéptido que comprende Gly-Ile； Xaa2 es Trp o un análogo de Trp； Xaa3 es His, Ala, Phe o Trp； Xaa4 es Thr, Thr, Ile, Val, Gly, o un tripéptido que comprende Thr-Ala-Asn, en la que un -OH en carboxi terminal de cualquiera de L-Thr, D-Thr, Ile, Val, Gly o Asn es opcionalmente sustituido por NH2； y los dos residuos de Cys están unidos por un puente disulfuro, en la que (a) el análogo de Trp en Xaa2 es un anillo aromático bicíclico sustituido o insustituido o dos o más anillos aromáticos monocíclicos sustituidos o insustituidos； o (b) el análogo de Trp
