AbstractKallikrein-related peptidases (KLKs), includingKLK5, have been proposed as promising biomarkers for prostate cancer diagnosis and prognosis. In the present study, we report that distinct augmentations (up to 6.4-fold) ofKLK5mRNA expressional levels, calculated via quantitative real-time PCR, occur after treatment of DU145 cells with appropriate concentrations, determined by the MTT method, of docetaxel and mitoxantrone. Our data reveal the endogenous need of prostate cancer cells for modifiedKLK5expression to cope with the administration of chemotherapeutic drugs. Furthermore, it is proposed that the expression profile ofKLK5could serve as a putative biomarker for monitoring the treatment response in hormone refractory prostate cancer patients.