This invention relates to nucleic acids encoding novel BPTI-homologous Kunitz domains, especially LACI homologues, which inhibit one or more plasma (and/or tissue) kallikreins, and to the therapeutic and diagnostic use of these novel proteins. In particular, the Kunitz domains are derived from Kunitz domains of human origin and especially to the first Kunitz domain of LACI. Additionally, the invention relates to recombinant expression vectors comprising a nucleic acid according to the invention, methods for producing a kallikrein binding domain, isolated polypeptides comprising a Kunitz domain structure, pharmaceutical compositions thereof as well as the use of the same and methods of assaying the presence of kallikrein or of purifying kallikrein.
