Parkinson's disease, a neurologic disorder characterized by a dopamine deficit within the striatum, may be improved by transplantation of polymer encapsulated neurosecretory cells. Surrounding cells with a selectively permeable barrier offers several advantages, including preventing immune rejection and tumor formation while allowing functional efficacy. Bovine adrenal medullary chromaffin cells, or PC12 cells, a rat-derived pheochromocytoma cell line, were encapsulated within polyelectrolyte-based microcapsules or thermoplastic-based macrocapsules. Histologic and biochemical analyses revealed that both types of cells survived and that neurotransmitter release from capsules was sustained for several months in vitro, irrespective of the encapsulation method employed. Both of the encapsulation systems protected the enclosed cells from an immunologic challenge in vitro, and prevented immune rejection when cell containing capsules were implanted in an immunologically incompatible host. Chromaffin or PC12 cell containing capsules implanted into the dopamine (DA) depleted striatum of rats reduced the lesion associated functional deficit. These results suggest that encapsulated neurosecretory cell implants may be useful in treating various central nervous system (CNS) deficits, particularly in cases involving a specific neurochemical lesion.