A Pseudomonas sp. strain NGK 1 (NCIM 5120) was immobilized in various matrices, namely, alginate, agar (1.8 x 10(11) cfu g(-1) beads) and polyacrylamide (1.6 x 10(11) cfu g(-1) beads). The degradation of naphthalene was studied. by freely suspended cells (4 x 10(10) cfu ml(-1)) and immobilized cells in batches, with shaken culture and continuous degradation in a packed-bed reactor. Free cells brought about the complete degradation of 25 mmol naphthalene after 3 days of incubation. whereas, a maximum of 30 mmol naphthalene was degraded by the bacteria after 3-4 days of incubation with 50 mmol and 75 mmol naphthalene, and no further degradation was observed even after 15 days of incubation. Alginate-entrapped cells had degraded 25 mmol naphthalene after 3.5 days of incubation, whereas agar- and polyacrylamide-entrapped cells took 2.5 days; 50 mmol naphthalene was completely degraded by the immobilized cells after 6-7 days of incubation. Maximum amounts of 55 mmol, 70 mmol and 67 mmol naphthalene were degraded, from an initial 75 mmol naphthalene, by the alginate-, agar- and polyacrylamide-entrapped cells after lj days of incubation. When the cell concentrations were doubled, 25 mmol and 50 mmol naphthalene were degraded after 2 and 5.5 days of incubation by the immobilized cells. Complete degradation of 75 mmol naphthalene occurred after 10 days incubation with agar- and polyacrylamide-entrapped cells, whereas only 60 mmol naphthalene was degraded by alginate-entrapped cells after 15 days of incubation. Further, with 25 mmol naphthalene, alginate-, agar- and polyacrylamide-entrapped cells (1.8 x 10(11) cfu g(-1) beads) could be reused 18, 12 and 23 times respectively. During continuous degradation in a packed-bed reactor, 80 mmol naphthalene 100 ml(-1) h(-1) was degraded by alginate- and polyacrylamide-entrapped cells whereas 80 mmol naphthalene 125 ml(-1) h(-1) was degraded by agar-entrapped cells.