The effects of fasting on the drug regimens of 81 Asian Moslem patients during the religious month of Ramadan have been examined. Twenty-two male and 15 female patients were found to change their drug dosage pattern while fasting: 35 missed doses; 8 took their tablets at different times and 4 patients took all their medication as one single daily dose after breaking fast in the evening. The consequences of these changes are discussed and ways in which the problems which arise may be overcome are examined.