Analysis of fish collected by the U.S. Fish and Wildlife Service for the fall 1970 National Pesticide Monitoring Program detected the presence of a compound eluting with, and subsequently identified incorrectly as B-benzenehexachloride. This compound was frequently observed when Florisil cleanup was used in the analysis of organochlorine residues in fish. Examination of selected sample extracts by gas chromatography-mass spectrometry (GC-MS), however, indicated that the compound was really hexachlorobenzene (C6CI 6 or HCB). After identification, residue levels were determined in fish collected from waters within the United States.