Numerous methods of immobilizing mammalian cells have been described in the literature (1). The practical benefits of immobilization include reuse of the biological catalysts (cells), increased product concentration, and protection of the cells from hostile environments. Systems such as microcarriers, gel entrapment, and microencapsulation in which the cells are retained, associate with, or adhere to small particles have been extensively studied for more than 10 years. One method which has shown to be particularly useful for culturing mammalian cells is microencapsulation. The mammalian cells are retained inside of a semipermeable hydrogel membrane. A porous membrane is formed around the cells permitting the exchange of nutrients and metabolic products with the bulk medium surrounding the capsules. The first practical method of microencapsulating viable mammalian cells was described by Lim (2) in 1978 and patented in 1982 (3). Since that time microencapsulation has been utilized for large-scale mammalian cell culture (4) and alternative methods of encapsulation have been developed.