AbstractStreptomyces phaeochromogenescells were immobilised by radiation polymerisation of hydrophilic monomers; highest levels of glucose isomerase activity were found in immobilised cell composites with highly hydrophilic polymer matrices. The enzyme activity in the composites from the copolymerisation of hydroxyethyl acrylate (or methacrylate) andN‐vinyl‐2‐pyrrolidone monomer increased markedly with increase in the content of theN‐vinyl‐2‐pyrrolidone monomer, owing to the higher water absorption by the polymer matrix, and was close to that of the non‐immobilised cells. The enzyme activity was affected by monomer concentration, the hydrophilicity, and chemical structure of the polymer matrix. The Michaelis constant of the composites from hydrophilic monomers was close to that of the