Diphenolases from Anoxybacillus kestanbolensis strains K1 and K4(T), highly active against 4-methylcatechol were characterized in terms of pH- and temperature-optima, pH- and temperature-stability, kinetic parameters, and inhibition/activation behaviour towards some general polyphenol oxidase (PPO) inhibitors and metal ions. The temperature-activity optima, for Anoxybacillus kestanbolensis K1 and K4(T) catecholases in the presence of 4-methylcatechol, were 80 and 70 degrees C, respectively. Although catecholase from A. kestanbolensis K4(T) lost no activity after a period of 1 h incubation at its optimum temperature, the enzyme from K1 was stimulated by keeping at 80 degrees C. Both of the enzymes possessed pH optima at 9.5, and the pH- stability profiles showed that cathecholases from both preparations retained their activities at alkaline pH values. Both A. kestanbolensis K1 and K4(T) catecholase activities were totally inhibited by addition of 0.01 mM sodium metabisulphite, ascorbic acid and L-cysteine. 1 mM Mn2+ increased the activities of A. kestanbolensis K1 and K4(T) catecholases by 6.4- and 5.3-fold, respectively. These results indicate that both A. kestanbolensis K1 and K4(T) strains possess thermo- and alkalostable catecholases.