Preliminary data in our research lab have shown that ursodeoxycholic acid (UDCA) inhibited the proliferation of polycystic human cholangiocytes in vitro through the normalization of the intracellular calcium levels in cystic cholangiocytes. The investigators also found that daily oral administration of UDCA for 5 months to PCK rats, an animal model of ARPKD that spontaneously develops hepato-renal cystogenesis, resulted in inhibition of hepatic cystogenesis.