This study will consist of three study periods separated from each other by a two weeks washout period. In the course of the study the subjects will receive in a double blind, crossover fashion, rifampin 300 mg. twice daily, diclofenac 50 mg twice daily. and fluconazole 200 mg. twice daily, each for one week. All drugs will be administered as identical looking tablets that will be prepared at the pharmacy of the Hadassah University Hospital and their order of administration will be randomized.On the day prior to, on day 6 of and 7 days following each drug period, the activity of CYP2C9 will be evaluated by the administration of a single phenytoin 300 mg. dose. The subjects will be requested to collect their urine for 24 hours and a single blood sample will be obtained 12 hours post phenytoin intake.