A method for immunoassay analysis of the organochlorine insecticide, hexachlorocyclohexane (HCH) has been developed, based upon alkaline conversion in standards and samples to trichlorobenzenes. The trichlorobenzenes were detected through antisera developed to haptens containing either a trichlorobenzene or trichlorpyridine moiety, developed using the herbicides, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and triclopyr, respectively. An enzyme conjugate based on 2,4,5-trichlorophenol provided most sensitive and specific detection. Although the assays cross-reacted with the herbicides, they did not suffer from the major disadvantage of extremely strong cross-reaction with cyclodiene organochlorines reported for a commercial HCH assay. The most sensitive assay had a lower detection limit of 20 w g l−1in drinking water and was applied to water and soil matrices.