Plasma or serum is diluted ten times with 0.1 M NaOH. Bile acids are extracted and purfied by passing the sample through a column of Amberlite XAD-2. The resin adsorbs the bile acids, which are then eluted with ethanol. After addition of sodium hydroxide and hydrolysis, the free bile acids are extracted by Amberlite XAD-2 and are then methylated and analyzed by gas chromatography. The degree of purification obtained in the first extraction step is sufficient to permit an analysis of conjugated bile acids or bile acid sulfates by thin-layer or Sephadex LH-20 chromatography.