During a screening for new microbial alpha-glucan phosphorylases corynebacteria were found to be promising, not-yet-identified producers of these particular enzymes. A maltodextrin phosphorylase (MDP) from Corynebacterium callunae was isolated, partially characterized, and used for the production of glucose-1-phosphate (G-1-P) from different a-glucans. In fermentor cultivations of C. callunae using maltodextrin as the inducing carbohydrate component, an MDP activity of approximately 8-10 units/g biomass (equivalent to 250 units/l) could be obtained. Contaminating activities of phosphoglucomutase and phosphatase were removed by ammonium sulphate precipitation followed by hydrophobic interaction chromatography on phenyl-sepharose. The partially (14-fold) purified MDP showed pH optima of 6.8 and 6.0 in the direction of phosphorolysis and synthesis, respectively. In the presence of 50 mM inorganic phosphate the enzyme was stable for more than 2 months at room temperature. The new MDP is capable of producing G-1-P from maltodextrins, soluble starch, and glycogen with decreasing order of activity. The same glucans were accepted as primers in the direction of synthesis. Increasing pH values favoured the formation of G-1-P and optimized conditions for its production were established at a pH of 7.5. The maximum attainable yields of G-1-P by the action of MDP are limited by mainly two factors : (1) no more than approximately 20% of the initial inorganic phosphate could be converted into G-1-P and (2) the highest degrees of phosphorolytic maltodextrin degradation were in the range 30-35%. These values could be increased to more than 60% after pretreatment of the maltodextrins with pullulanase.