Levels of plasmin activity in various commercial cheeses are reported. The effects of some processing conditions (pH, cooking temperature and method of salting) on plasmin activity in cheese were investigated. Neither draining pH nor method of salting affected the activity. However, plasmin activity in cheese, rennet curd and micellar casein dispersions increased with increasing cooking temperature. The results suggest that plasmin activity in cheese depends on cooking temperature used during manufacture. © 1990, Proprietors of Journal of Dairy Research. All rights reserved.