Pseudomonas sp. BA2 showing L-aminoacylase activity was immobilized by entrapment in calcium alginate gel. To enhance operational stability, the immobilized cells were treated with hardening reagents using four different methods : treatment of the cells with glutaraldehyde before immobilization, stabilization of the immobilized cell preparation with glutaraldehyde or glutaraldehyde and hexamethylenediamine, and finally activation of the alginate solution with periodate followed by treatment with polyethyleneimine. Very active and stable immobilized cell preparations were obtained when Pseudomonas sp. BA2 cells immobilized in calcium alginate were treated with 20 mM glutaraldehyde. Compared with the untreated preparation, the enzymatic activity was markedly increased (132%) and the half-life period was increased by 4 h. Moreover, the suitability of the biocatalyst for reuse in batch processes was noticeably improved (only 60% of the initial L-aminoacylase activity was lost after four runs). When the immobilized and stabilized cell preparation was used for L-alanine production in a continuous stirred-tank reactor substrate conversion at the reactor outlet was higher than that obtained with the untreated beads. The reactor production after 33 h was 61 of 17 mM L-alanine solution (9 g of optically pure amino acid) more than double that obtained using the untreated immobilized cells, and significantly higher than those previously reported in the literature.