In cholestasis, serum lipids are altered. The alterations could at least partially be ascribed to the occurrence of an abnormal lipoprotein, LP-X. In 103 patients with jaundice, out of whom 16 had extra-hepatic cholestasis, the presence of LP-X was tested and semi-quantificated (by visual grading) utilizing an immunological technique. In extra-hepatic cholestasis, all patients showed LP-X in serum, while in intra-hepatic drug-induced cholestasis 87% revealed this phenomenon. At the initial stage of acute hepatitis, in drug-induced cholestasis, and in extra-hepatic cholestasis, the semi-quantificated LP-X correlated with alkaline phosphatase values. In extra-hepatic cholestasis, LP-X disappeared soon after the obstruction was relieved by operation.