Metabolic experiments of lindane and related compounds are reviewed. Lindane and other BHC isomers produced 2, 4, 6-trichlorophenol as the major oxidative metabolite by rat liver microsomes. A mechanism was shown to be direct oxygenation of the cyclohexane ring followed by dehydrochlorinations. Microsomes from rat liver and housefly abdomen effectively metabolized lindane to (36/45)- and (346/5)-pentachlorocyclohexene and (36/45)-hexachlorocyclohexene in addition to 2, 4, 6-trichlorophenol. A reaction mechanism was proposed which includes electrophilic attack by an activated oxygen to chlorine or hydrogen. Microsomes metabolized isomers of tetra-, penta-, and hexachlorocyclohexene to tetrachlorocyclohexenol isomers, 2, 4, 5-trichlorophenol and 2, 3, 4, 6-tetrachlorophenol, respectively. The (346/5)-isomer of pentachlorocyclohexene also gave an abundant amount of pentachlorocyclohexenol isomer. These oxidative reactions were shown to proceed mainly via ene-like hydroxylation accompanied by double bond migration. Reductive dechlorination of lindane and related polychlorocyclohexenes under anaerobic condition was found using microsomes and NADPH. 1, 2, 4-Trichlorobenzene was produced abundantly from (36/45)-hexachlorocyclohexene in this condition. Correlations of this biochemical reductive dechlorination with electrochemical reduction were illustrated. 4-Chloro-, 2, 4-dichloro-, 3, 4-dichloro-, 2, 3, 5-trichloro- and 2, 4, 5-trichlorophenylmercapturic acids were identified as the main mercapturic acid metabolites of lindane. Their formation from (346/5)-tetra-, (346/5)-penta-, (36/45)-penta-, and (36/45)-hexachlorocyclohexene was proposed based on in vitro experiments using rat liver soluble fraction and glutathione. A mechanism was proposed which includes substitution by glutathione of allylic chlorine with or without double bond migration. All these findings elucidated the in vivo metabolic pathways of lindane degradation in the rat and in the housefly.