A deficit in gamma-aminobutyric acid (GABA) levels in the brain or the cerebrospinal fluid (CSF) is found in many epilepsy patients. Frequency and severity of seizures may be reduced by treatment with GABA increasing medicaments as e.g. vigabatrin, an irreversible inhibitor of GABA-transaminase. For a better understanding of the associated effects, healthy volunteers were examined with magnetic resonance spectroscopy (MRS) and positron emission tomography (PET) before and after intake of different doses of vigabatrin. For the MRS examinations, a dedicated localized spectral editing method was developed to determine GABA levels. The 11C-flumazenil (FMZ)-PET protocol allowed determination of GABA-A receptor binding. The results show a clear and dose-dependent increase in the brain GABA levels after the medication period as compared to the baseline values. The GABA-A receptor binding, on the other hand, did not change significantly.