The importance of the Jun N‐terminal Kinase (JNK) pathway during normal development and tumor invasion has been well documented inDrosophila. Here, this pathway plays important roles in epithelial morphogenesis, wound healing, apoptosis, immunity and regulation of lifespan. However, which downstream molecules facilitate these effects is not very well elucidated. In this study, data are presented on a serine protease homolog (SPH),scarface. These data show thatscarface is under regulatory control of the JNK pathway and that this pathway is both necessary and sufficient for its expression within the context of thoracic development. Consequently, down‐regulation ofscarface results in a thoracic‐cleft phenotype that phenocopies the JNK pathway defect. A possible role ofscarface during thoracic development inDrosophila is discussed.