Attempts were made to isolate the causative substance of poisoning due to ingestion of carp, Cyprinus carpio. Patients develop complex symptoms including acute renal failure, liver dysfunction, paralysis and convulsions of limbs, etc. The bile from carp was extracted with 80% methanol under reflux. The extract was defatted with chloroform, ultrafiltered, and subjected to an Amberlite XAD-2 treatment. The unbound fraction was subjected to silica gel 60 and SEP-PAK C₁₈ cartridge chromatographies. The obtained toxin was further purified by high performance liquid chromatography on a D-ODS-5 column. The purified toxin was homogeneous in thin-layer chromatography, and showed a minimum lethal dose of 2.6mg/20g mouse. The molecular weight of this toxin was determined to be 532 by fast atom bombardment mass spectrometry. Based on the results of TLC and IR spectrometry, this toxin was supposed to be a steroid-related substance, having a sulfate ester group in the molecule.