The limitations of the new drug development process, particularly in regard to the evaluation of drug safety, have resulted in a need for monitoring drug experience in the postmarketing period. Although a number of systems have evolved to perform postmarketing surveillance, each has important limitations, suggesting the need for an alternative, innovative approach that would permit rapid identification of potential problems and support studies of multiple drugs and/or disease states in patient populations large enough to permit identification of uncommon, but significant adverse drug reactions. This has led to the organization of a nationwide network of clinical pharmacists with an active role in patient-care monitoring to collect information regarding the safety and effectiveness of drugs. At the present time there are 383 clinical pharmacists from all 50 states participating in the network. These individuals collectively monitor more than 150,000 inpatient hospital beds, more than 40,000 nursing home beds, and more than 800,000 ambulatory care visits per year. Participating clinical pharmacists, using standardized data collection forms, perform concurrent monitoring of drug-therapy outcome in targeted patient populations. Careful analysis and interpretation of this information will yield clinically relevant information regarding the outcome of drug therapy under actual clinical conditions.