A new high-water-content (83%) and highly permeable anionic polyelectrolyte hydrogel was obtained by phase inversion of a polymer solution containing 6% polyacrylonitrile-sodium methallylsulphonate, 91% dimethylsulphoxide and 3% physiological saline solution. Hydrogel-based hollow fibres (HFs) were fabricated with a co-extrusion apparatus in collaboration with Hospal (France). HFs have an internal diameter of 800 microns and a wall thickness of 100 microns. Experimental results demonstrated that hydrogel-based HFs were permeable to albumin (mol. wt 69,000) and human immunoglobulin G (150,000), but were impermeable to immunoglobulins A (170,000) and M (900,000) after 24 h of diffusion. In vitro, the viability of isolated rat hepatocytes injected into the HFs was 64 +/- 6% after 10 d versus 30 +/- 5% for hepatocytes cultured in Petri dishes (P = 0.0001). Under these conditions, the amount of albumin released by encapsulated hepatocytes was 12 +/- 3 micrograms/24 h/10(6) cells at day 10, whereas at that time no albumin was released by hepatocytes cultured in Petri dishes. In vivo, histological study of hydrogel HFs implanted up to 6 wk in the peritoneum of rats revealed a low inflammatory tissue reaction without giant multinucleate cells in the foreign tissue, which decreased after the third week. The survival rate of encapsulated hepatocytes was over 85% 45 d after transplantation in the peritoneum of syngeneic Lewis rats. Therefore, this hydrogel demonstrates highly favourable properties for encapsulation of hepatocytes with regard to its biocompatibility, permeability and ability to maintain hepatocytes in a functional state for prolonged periods.