El mice are epileptic mice in which convulsive seizures are easily induced by throwing stimulation. Uptake and release of [(3)H] 5-hydroxytryptamine and [(3)H] taurine were examined in cerebral cortical slices of non-stimulated El mice [El(-)], stimulated El mice [El(+)] during the interictal period and ddY mice (ddY), which are the mother strain of El mice and do not have a convulsive disposition. Release was defined as 40mMK(+)-stimulated release. Uptake of 5-HT and taurine was lower in El(+) than in El(-), but no significant difference was found between ddY and El(-). Release of 5-HT and taurine was higher in El(-) than in either ddY or El(+). No significant difference in spontaneous release of 5-HT and taurine was found between ddY, El(-) and El(+). The taurine level in El(-) and El(+) was higher than in ddY, but no significant difference was found between El(-) and El(+). These results suggest that low uptake and release of 5-HT and taurine may increase seizure susceptibility in El(+).