Pseudomonas sp. strain M285 immobilized on diatomaceous earth beads was used to remove 3,5,6-trichloro-2-pyridinol (TCP) from industrial wastewater. Batch studies showed that immobilized Pseudomonas sp. strain M285 mineralized [2,6-C-14]TCP rapidly; about 75% of the initial radioactivity was recovered as (CO2)-C-14. Transformation of TCP was inhibited by high concentrations of salt, and addition of osmoprotectants (proline and betaine at 1 mM) did not reduce the adverse effect of salt. TCP-containing wastewater (60-140 mg/l) was passed through columns containing immobilized Pseudomonas sp. strain M285 at increasing flow rates and increasing TCP concentrations; TCP removal of 80%-100% was achieved. Addition of nutrients, such as glucose and yeast extract, retarded TCP degradation. Growing cell cultures were found to be better inocula for immobilization than resting cells.