Genetically conditioned change in activity of SSRI metabolizing enzymes may lead to different therapeutic response of patients, ranging from lack of efficacy to symptoms of toxicity and a significant incidence of drug-drug interactions. The activity of P 450 cytochromes can be determined by genotyping or phenotyping. CYP2D6, cytochrome P-450 isoenzyme, is a catalyzing enzyme of a number of frequently used SSRI and has been known to be genetically polymorphous. The goal of the study was to evaluate the efficacy of paroxetine treatment in female patients with mental bulimia (MB) while monitoring CYP2D6 activity