Conidiobolus coronatus (NCL 86.8.20) produces high levels of protease activity (30 U ml(-1)). The ease of microbe-free enzyme preparation and its compatibility with most of the commercial detergents are the advantageous features of Conidiobolus protease. The enzyme was stable at 28 degrees C for 20 h and at 40 degrees C for 1 h, but was completely inactive on incubation at 50 degrees C for I h. Higher thermostability is an important factor for the suitability of its application in detergents. The effect of a wide variety of compounds was studied to enhance the thermal stability of the protease by modification of its microenvironment. Urea (2-4 M), sodium dodecyl sulfate (1%), NaCl (200 mM), and beta-mercaptoethanol (10 mM) did nor improve the stability of the enzyme. Ethylene glycol (10%), glycerol (1%), sorbitol (800 mM), and PEG-8000 (200 mM) had a marginal effect in preventing the thermal inactivation of the protease. Casein (0.5%) was also unable to increase the stability of the enzyme at 50 degrees C. Addition of Ca2+ (25 mM) or glycine (1 M) was effective in increasing the half-life of the enzyme three-fold. The enzyme retained 43% of its activity at 50 degrees C in the presence of Ca2+ and glycine. The enzyme showed compatibility at 50 degrees C with commercial detergents such as Revel and Ariel in presence of Ca2+.