Different matrices viz. agar. alginate and polyacrylamide were examined for the immobilization of whole cells of Ralstonia pickettii. The enzyme activity of whole cells immobilized in agar beads was very low. Alginate beads had the inherent disadvantage of dissolving in phosphate based media and even glutaraldehyde treatment did not have any significant effect. A Tris-HCl system was found to be the best for alginate based immobilization of whole cells from R. pickettii and 4% alginate beads gave an optimal lipase activity of 14 U/ml per min. When different concentrations of polyacrylamide were tried for immobilization of R. pickettii whole cells, 15% polyacrylamide blocks showed a retention activity of 66% (25 U/ml per min) when compared to that of the free cells (40 U/ml per min). Bis-acrylamide concentration of 0.15 g/10 ml of buffer was ideal and the optimum whole cell concentration for polyacrylamide immobilization was 2.0 g/l of saline. Optimal immobilized whole cell concentration (polyacrylamide blocks) for lipase production was 20% and polyacrylamide blocks were reused three times effectively for lipase production. Of the three matrices examined for the immobilization of whole cells from R. pickettii polyacrylamide gave the best performance. (C) 2001 Elsevier Science Ltd. All rights reserved.