A prospective study of adverse drug reactions was recently completed at the Clinical Pharmacology Unit of J. J. Group of Hospitals. 338 patients were included in this study, and adverse reactions were noted by a team of workers including a nurse and a physician. World Health Organization definitions were used to describe adverse reactions. A total of 20 per cent of the patients showed adverse reactions to drugs. There was no difference with regard to age, occupation, or religion of the patients. Reaction was more common in the undernourished and also with a larger number of drugs or longer duration of stay in the hospital. The common reactions were neurologic, gastrointestinal, and allergic. Significant information is obtained by analysis of the percentage reaction in patients receiving drugs and the percentage of reactions per doses administered. It is confirmed that short-term intense surveillance programs are capable of providing useful data on incidence and types of adverse drug reactions.