Appears to lack serine protease inhibitor activity in vitro when tested with bovine pancreatic alpha-chymotrypsin and elastase (PubMed:19716386). Involved in cuticle biosynthesis (PubMed:16500660, PubMed:19716386). Expressed in larval and adult hypodermis, hermaphrodite vulva and adult excretory cell and duct. Expressed at low levels in larvae and adults. Expression increases during L2-L3 molting stage an prior L3-L4 molting stage. RNAi-mediated knockdown causes blisters in the cuticle and abnormal localization of collagen col-19 in cuticle dorso/ventral annulae and lateral alea. Appears to have serine protease activity in vitro (PubMed:19716386). However, it is uncertain if this activity is genuine as bli-5 lacks all the catalytic features of serine proteases.