SphereZymes ä are self-immobilised enzyme particles that are formed by cross-linking enzymes while in an emulsion. The resultant spherical particles can be isolated and applied in biocatalytic reactions.Modifi cation of the cross-linking procedure to utilise a polyamine polymer (polyethyleneimine), in conjunction with glutaraldehyde, enhanced the activity of Alcalase ® SphereZyme preparations towards both large (azocasein) and small substrates ( p -nitrophenyl acetate), resulting in 16.6% and 53.7% retention in the activity, respectively, after immobilisation. To improve the fi lterability of these particles, we attempted two strategies. One was to include rigid polyethyleneimine -silica particles in the SphereZymes, and the second was to entrap SphereZymes in rigid PVA hemispheres (LentiKats ® ). Both methods greatly enhanced the fi lterability and robustness of the SphereZymes, with the entrapped particles being the easiest to handle.