We have recently identified a gene (the WFIKKN gene) on human chromosome 16 (16p13.3) that encodes a secreted protein containing WAP-type, Follistatin/ Kazal type, Kunitz-type and NTR-type protease-inhibitory modules and an Immunoglobulin domain [Trexler et al., Proc. Natl. Acad. Sci. USA 98 (2001), 3705 - 3709]. In the present work we show that a gene on chromosome 17 encodes a WFIKKN-related protein (WFIKKNRP) that has the same domain organization as the WFIKKN protein. The exon-intron structure of the two genes is also similar as both genes have a single phase 0 intron that splits their WAP domains in equivalent positions. In view of the presence of several protease inhibitory modules in these proteins it seems likely that they serve to control the action of multiple types of proteases. The tissue expression pattern of the two proteins, however, is markedly different suggesting that they have distinct biological roles. Whereas the WFIKKN gene is expressed primarily in adult pancreas, liver and thymus but not in brain and ovary, significant expression of the WFIKKNRP gene is observed in ovary, testis and brain, but not in liver. Pronounced differences could also be seen in the case of fetal tissues: expression of the WFIKKN gene was highest in the lung, skeletal muscle and liver, whereas the WFIKKNRP gene was expressed primarily in brain, skeletal muscle, thymus and kidney.