Various industrially used protein substrates were hydrolysed by a recently constructed, thermally stable, thermolysin-like protease variant (Boilysin; Van den Burg et al., Proc. Natl. Acad. Sci. 95: 2056-2060) and three industrial protease preparations. Hydrolysates were analysed by measuring the acid-soluble products and by SDS-PAGE of the breakdown products. The rate and extent of hydrolysis obtained by Boilysin was, in most cases, higher than those obtained with the three commercially available enzyme preperations tested. This suggests that protein hydrolysis with this new protease variant at elevated temperatures can result in improved substrate conversions.