Ongoing monitoring of the availability of hospital critical care resources is necessary to assure patients in the emergency medical services (EMS) system reach appropriate care. In this densely populated area Multnomah County, Oregon, ambulances have been diverted by radio from several hospitals before finding one that would accept the patient. Dispatch centers and base-stations had no reliable method to monitor the availability of hospital resources. Data were not available for use in establishing policy. In response, this community developed an on-line, computerized system known as Computerized Hospital On-Line Resources Allocation Link (CHORAL) that visually displays the resource status of all hospitals to the 911 center, base station, and participating hospitals. A change of status requires simple keystrokes for entry into the computer which in turn transmitted automatically to all other CHORAL computers. Six patient care resources are monitored: Adult Ward (AW); Computerized Axial Tomography Scan (CT); Critical Care (CC); Labor and Delivery (LD); Pediatric (PEDS); and Psychiatric Secure Beds (PSB). Paramedics use protocol to determine if a particular patient fits one of these categories. Availability is relayed to paramedics by the 911 center and the base-station. During the first three months of system operation, there were 337 diversions representing 4,527 hours among 10 of the 12 participating hospitals. The most common resource resulting in diversion was PSB, which was unavailable for 2,195 hours (48.5%). Unavailability of CT resulted in the lowest number of diversions (1.3%, 60.3 hours).(ABSTRACT TRUNCATED AT 250 WORDS)