Current quality assurance practices forUHTmilk include sterility checks, which, in total, can take 10 days.As proteases are a major cause of defects in UHT milk, testing should also be carried out for the activity of these enzymes. The result of such tests would indicate the extent of protease contamination and provide information to aid in estimating the shelf life of the UHT milk. Protease assays based on FITC-casein as substrate with long incubation times (up to 14 days) can detect very low levels of protease. These assays are suited to quality control programs for UHT milk. Assays based on casein are less sensitive but correlate well with potential proteolysis in UHT milk and may be a cost-effective alternative for routine testing.