Postmarketing surveillance (PMS) studies allow for the systematic and comprehensive monitoring of the beneficial and harmful effects of prescription drugs as well as their usage patterns. The objectives of PMS are to assess the uses and effects of new drugs under conditions of customary clinical use. The following methods are used to assess new drugs under these conditions: 1. the publishing of case reports describing a new adverse effect, drug-drug interaction, or an unexpected response to a drug; 2. voluntary adverse drug reaction reporting; 3. registries; 4. hospital-based intensive monitoring; 5. case-comparison studies; and 6. prospective cohort studies. The Upjohn Company, under the rubric of the Medication Monitoring Program, utilizes pharmacists extensively to recruit outpatients for nonexperimental comparison cohort studies of its products. Numerous other PMS functions are being carried out by pharmacists in hospital settings. The cooperation of pharmacists and sponsors of PMS is essential in order to maximize the knowledge about medications and their users.