A rat pheochromocytoma cell line (PC12) was encapsulated in a water-insoluble hydroxyethyl methacrylate-methyl methacrylate copolymer by interfacial precipitation from a polyethylene glycol 200 solution into phosphate-buffered saline. The resulting capsules (660 +/- 44 microns in diameter; 84 +/- 27 microns wall thickness) contained viable PC12 cells in a spheroidal arrangement, much like tumour spheroids, the latter grown on surfaces unsuitable for cell attachment. In these spheroids, the viable cells formed a band approximately 100 microns thick, surrounding an inner core of necrotic cells. A similar arrangement was seen 14, 28 and 42 days after encapsulation, with capsules maintained in an in vitro tissue culture environment; the annular ring was roughly constant in size, although the packing density appeared to increase over the 6 week observation period. During the first 4 weeks, when measurements were made the encapsulated cells converted a tetrazolium dye (MTT) into an insoluble formazan product, in a time-after-encapsulation-dependent manner. This indicated that PC12 cells retained viability despite encapsulation and an ability to increase (at least in part) their metabolic capacity, presumably by a combination of proliferation and altered cellular activity. The encapsulated PC12 cells also secreted dopamine when incubated in a high potassium release medium but not in a low potassium, conventional tissue culture medium (RPMI 1640). Consistent with the MTT results, the amount of dopamine released was also dependent on the time after encapsulation, as well as the cell density at the time of encapsulation.