Reactive, macroporous and beaded glycidyl methacrylate-divinyl benzene copolymers of controlled particle size were synthesised. The role of crosslink density, pore generating solvent type and its volume, concentrations of protective colloid and polymerisation initiator on the efficacy of reacting with penicillin G acylase were investigated. The covalent binding and expression of bound penicillin G acylase was found to be altered by the different synthesis variables. Immobilised enzyme activity of 205 IU g(-1) was obtained with a polymer with 25 mol% crosslinking having a mean pore radius of 10.8 nm, generated with 43.5 cm(3) of cyclohexanol as porogen.