We have isolated a Pseudomonas sp. (strain SB15) which produces an isoamylase (EC 3.2.1.9). Highest yields of this enzyme were obtained when the bacterium was grown in shaken culture in a medium containing maltose, dextrin, starch, or isomaltose. Specific carbon and nitrogen sources were required for growth. The most satisfactory medium consisted of 2% maltose, 0.4% sodium glutamate, 0.3% diammonium hydrogen phosphate, and other inorganic salts. The optimal pH for enzyme production was 5 to 6. The enzyme is stable between pH 3 and 6 but is extremely labile above pH 7. It splits amylopectin completely by combined action with β-amylase but does not attack pullulan. Images