Epilepsy is characterized by seizures recurring at interindividually differing time intervals. It may be difficult to assess drug response if time intervals between seizures are long. Thus, the existence of surrogate parameters that could be used to reliably identify drug efficacy and tolerability at an early stage and also as prognostic factors would be desirable. Electroencephalography, magnetic resonance imaging, and genetic markers are the domains to be assessed in this respect. The availability of clinically useful pharmacodynamic parameters is, however, currently disappointing.