Abstract. A large number of hepatoma cell lines has been used to study expression and regulation of liverspecific function . However these cells, even the most differentiated, are morphologically far from hepato cytes. In no case is the typical hepatocyte cell polarity well maintained.Cell hybridization has been used as a potential means for turning on specific genes . From hybrids between well differentiated Fao rat hepatoma cells and WI 38 human fibroblasts, we have attempted to isolate segregated cells that are highly differentiated and polarized. Such cells, detected in aged cultures of only one hybrid (WIF12), were isolated by subcloning. One subclone, WIF12-1 was analyzed .Expression of liver-specific functions extinguished in the original hybrid is restored in all WIF12-1 cells at a very high level, similar to that of hepatocytes and

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