Pseudomonas sp. IMD 353, secretes an extracellular maltotetraose-producing amylase. One of the most outstanding features of this enzyme is that it is produced constitutively (29 units/ml), using glucose (3%, w/v) as the carbon source. The amylase was purified to homogeneity and its enzymic properties examined. It had maxima for activity at pH 7.0 and 50 degrees C, a relative molecular mass of 63,000 and an isoelectric point at pH 5.0. Specific amylase inhibitors, tendamistat and alpha-amylase wheat inhibitor, activated the enzyme. Starch was hydrolysed from the non-reducing chain ends, by an endo-acting mechanism, producing maltotetraose in the alpha-anomeric form. Yields of 65% (w/v), and 62% (w/v) were obtained on hydrolysis of starch (1%, w/v) and dextrin (15%, w/v), respectively. This enzyme failed to hydrolyse maltotetraose, even on prolonged incubation.