Methods and materials are disclosed for the production of purified, active recombinant human neutrophil protease, PR-3, via activation of a pro-form herein referred to as proPR-3. Human PR-3 is useful for discovering inhibitors of excessive release of mature, active TNF.alpha.. Also disclosed are methods for the identification of inhibitors of the conversion of the pro-form of TNF.alpha. to its mature active form.