The effects of three isomers (alpha, beta, gamma) of hexachlorocyclohexane on the acquisition and expression of kindled amygdaloid seizures were compared. Treatment with corn oil (vehicle) was compared with daily 5 mg/kg doses of the isomers for 15 days during kindling procedures. The results confirmed the proconvulsant action previously described for the gamma-HCH isomer (lindane). Alpha-HCH did not produce significant effects. Rats treated with beta-HCH exhibited delayed rates of kindling acquisition and less severe seizures. Exposure to beta-HCH (5, 10 and 20 mg/kg) daily produced a dose-dependent decrease in the rate of kindling acquisition, seizure severity and afterdischarge duration. The differences were still manifest during an additional 20 kindling trials after beta-HCH administration had stopped. It is concluded that significant differences exist among the isomers of HCH with respect to their effects on the mammalian central nervous system and their effect in the kindling model of epilepsy. The availability of stereoisomers possessing different actions on kindling should make these compounds useful for discriminating between non-specific changes induced in membranes or at binding sites and specific changes correlated with proconvulsant or anticonvulsant effects in the kindling model.