There have been several reports of the isolated occurrence of raised serum gamma GT levels in the course of long-term anticonvulsive treatment. The findings concerning the correlation between this elevation of gamma GT and various dimensions of epilepsy or treatment regimens are equivocal. In a retrospective study of 158 epileptics, the mean values of the serum gamma GT level have been grouped according to anticonvulsive regimen and compared with one another, as well as correlated to the serum concentration of the antiepileptic drug. An elevation of serum gamma GT was found in 103 patients. Among the different subgroups the mean value for serum gamma GT was raised in cases under treatment with PHT, PB or PRM. No such elevation was found in cases under monotherapy with CBZ or VPR. The elevation of serum gamma GT is considered to reflect hepatic enzyme induction rather than hepatic impairment.