alpha -Amylases from the thermophilic fungus, Thermomyces lanuginosus ATCC 34626 (wild and mutant strains), were purified to homogeneity by a simple procedure including, consecutively, precipitation with ice-cold 2-propanol, anion-exchange and molecular-sieve chromatographic methods. The molecular masses of the purified alpha -amylases (both with pI values of 3.0) were 58 kDa by SDS-PAGE. The optimal pH of alpha -amylase activity was 5.0 for the wild enzyme and 4.5 for the mutant one. 1-Cyclohexyl-3-(2-morpholinyl-4-ethyl)-carbodiimide (40-100 mM) and N-bromosuccinimide (0.1-1 mM) inhibited the enzymes, suggesting the involvement of carboxylic groups and tryptophan residues in the catalytic process.