Four major bilirubin species in serum were separated by micellar electrokinetic chromatography with 25 mM sodium dodecyl sulfate (SDS) and 20 mM sodium tetraborate-boric acid buffer at pH 8.5. Due to the solubilization of the serum proteins by the SDS micelles, serum samples were injected directly into a 50 cm x 75 microns I.D. fused-silica capillary and complete separation of the four bilirubin species was accomplished within ca. 10 min without extensive sample pretreatment. Detection was performed by absorbance at 450 nm and average limit of detection was in the 6.0 microM concentration range. The usefulness of this method was demonstrated for the separation and detection of a number of bilirubin species present in pathological human serum samples.