In this study we measured biliary cytosolic calcium and examined the effect of cholestatic bile acids LCS and TLCS on intrahepatic isolated biliary cells cytosolic calcium. Cells have been isolated from bile duct ligated rats. Cytosolic calcium has been measured by using the Ca++ sensitive indicator Fura 2 and a cytofluorimetric method. LCS and TLCS (200 microM and 300 microM) increased the cytosolic Ca++ concentration of the cells. In contrast, the bile acids cholate and urso-desoxycholate which are choleretic had no effect. The number of cells which have increased their cytosolic calcium was directly correlated with the biliary acid toxicity. The increase induced by LCS and TLCS was abolished by removing external calcium. It is suggested that the calcium increase results from external calcium influx. This cytosolic calcium increase is known to be toxic for cells so it is concluded that this calcium increase is probably involved in the toxicity of LCS and TLCS.