Calcium alginate beads were used to entrap a Bacillus sp. that has the ability to biosorb cadmium. During the batch incubation of alginate beads in a 'rich' or a 'poor' liquid medium, cell release out of the beads was noticed with a lag phase which was inversely proportional to the inoculum size (2 x 10(7) or 2 x 10(8) cells ml(-1) alginate), to the medium content, and proportional to the alginate concentration (10 or 15 g l(-1)) and to the cadmium concentration (1, 5 or 10 mg l(-1)). In addition, the cell release occurred more quickly when the medium was renewed. When the concentration was below 5 mg l(-1), the alginate matrix seemed to protect the bacteria against Cd2+ toxicity.