A process designed for the efficient entrapment of whole cells should allow for: (1) High retention of cell viability; the biological activity of the entrapped cells should not be impaired by the immobilization conditions. (2) The porosity of the formed gel should be uniform and controllable. Free exchange of substrates, products, cofactors, gases, and so forth is essential for efficient performance of the immobilized cells. (3) The gel obtained should retain good mechanical, chemical, and biological stability. It should not be easily degraded by enzymes, solvents, pressure changes, or shearing forces. (4) The gel should be composed of reasonably priced components and the process should be amenable to ready scaling up. In view of the requirements, a method for whole cell immobilization via controlled chemical crosslinking of prepolymerized polyacrylamide-hydrazide was developed. In the following, the principle of this method is presented and its application for whole cell and enzyme immobilization is described.