The removal of Remazol Blue and Reactive Black B by the immobilized thermophilic cyanobacterial strain Phormidium sp. was investigated under thermophilic conditions in a batch system, in order to determine the optimal conditions required for the highest dye removal. In the experiments, performed at pH 8.5, with different initial dye concentrations between 9.1 mg l(-1) and 82.1 mg l(-1) and at 45 degrees C, calcium alginate immobilized Phormidium sp. showed high dye decolorization, with maximum uptake yields ranging from 50% to 88% at all dye concentrations tested. When the effects of high dye concentrations on dye removal were investigated, the highest uptake yield in the beads was 50.3% for 82.1 mg l(-1) Remazol Blue and 60.0% for 79.5 mg l(-1) Reactive Black B. The highest color removal was detected at 45 degrees C and 50 degrees C incubation temperatures for all dye concentrations. As the temperature decreased, the removal yield of immobilized Phormidium sp. also decreased. At about 75 mg l(-1) initial dye concentrations, the highest specific dye uptake measured was 41.29-41.17 mg g(-1) for Remazol Blue and 47.69-43.82 mg g(-1) for Reactive Black B at 45 degrees C and 50 degrees C incubation temperatures, respectively, after 8 days incubation. (C) 2007 Elsevier B.V. All rights reserved.