Rats were treated orally with technical hexachlorocyclohexane (HCH, 12.5, 25 and 50 mg kg-1 day(-1)) and technical isoproturon (ISP 22.5. 45 and 90 mg kg-1 day(-1)) daily for a period of 90 days alone and in combination. Treatment with HCH alone showed mild to severe toxicity and death. Significant changes occurred in liver weight, clinical enzyme profiles, haematological parameters and pathomorphological changes. Treatment with ISP alone did not produce such changes. The combination of HCH and ISP produced changes not suggestive of synergism.