Serum neuron-specific enolase (s-NSE) and s-100 protein (s-100) are sensitive markers of various brain diseases. We investigated both of these markers in nine patients within 5 min, 6 h, 12 h, and 48 h after a single tonic-clonic seizure. The mean peak s-NSE level was significantly higher after 5 min (11.97 +/- 8.56 mu g/l) and 48 h (10.31 +/- 8.92 mu g/l, P < 0.05) than the levels of seizure-free, age-matched controls. Five patients had increased s-NSE levels regarding the upper limit of normal as mean + 3 SD. s-100 was not detected either in controls or epileptic patients. These data indicate that s-NSE in contrast to s-100 may be an in vivo marker after generalized seizures in some patients.