A strain of Flavobacterium capable of producing an extracellular thermostable isoamylase which grew with optima at pH 6.0 and 30 degrees C was isolated from soil. Maximum enzyme production was observed with the medium (pH 5.3) composed of 3% (w/v) soluble starch, 3% soybean protein, 0.01% Na hydrogen L-glutamate, 0.14% KH2PO4, 0.02% MgSO4 . 7H(2)O, and 0.01% CaCl2 . 2H(2)O after 48 h of cultivation at 30 degrees C under aerobic conditions. The thermal stability of the enzyme in the presence of Ca2+ increased remarkably with trehalose and maltooligosaccharides. Maltotriose and maltotetraose were the most effective for stabilization against heating. Although a higher yield of condensed products was obtained with larger saccharides, the condensation of various linear maltooligosaccharides by the enzyme was significantly lower than that by the Pseudomonas isoamylase, and no condensed products were formed from trehalose by either enzyme. Addition of the Flavobacterium isoamylase remarkably enhanced the production of maltose, maltotroise, maltoteraose, and trehalose under industrial conditions for starch processing in the presence of respective auxiliary enzymes because of its lower transfer and condensation actions when compared with those of the Klebsiella pullulanase. These enzymatic characteristics are consistent with the industrial production of various saccharides from starch.