Several enzymes (aldolase, aminoacylase, arginase, carboxypeptidase B, cholinesterase, cyclodextrin glycosyltransferase and glucoamylase) were immobilised by covalent coupling on polyacrylamide bead polymers possessing carboxylic functional groups activated by water-soluble carbodiimides. The factors influencing the immobilisation process were studied. The catalytic activities of the immobilised enzymes were influenced advantageously by the structure of carbodiimide used as coupling agent. Immobilised enzymes of highest catalytic activity could be obtained if the carbodiimide was introduced into the reaction mixture in a stoichiometric quantity relative to the carboxylic functional groups located on the support and the support/protein ratio was from 1:0.25 to 1:1. It was found that the hydrogen ion concentration of the coupling reaction mixture has a profound effect on the immobilisation of enzymes. In the function of the ionic strength of coupling reaction mixture, the catalytic activity of immobilised enzyme produced showed an apparent optimum. The increasing porosity of support was favourable for the immobilisation of enzymes. The insertion of a spacer in the support appeared to be disadvantageous for the enzyme immobilisation.