The support systems for the Emergency Medical Services (EMS) in the mass gatherings, such as the local marathon or the large international baseball games, had been underdeveloped. The purposes for this study were to develop triage-based EMS Personal Digital Assistant (PDA) support systems for the mass-gatherings and to evaluate users' perceived ease of use and usefulness of the systems in terms of Davis' Technology Acceptance Model (TAM). The systems were developed based on an established intelligent triage PDA support system and two other forms-the general EMS form from the Taipei EMT and the customer-made Mass Gathering Medical form used by a medical center. 23 nurses and 6 physicians in the medical center, who had ever served in the mass gatherings, were invited to examine the new systems and answered the TAM questionnaire. The results showed that the PDA systems included as many 450 information items inside 42 screens under 6 categories and the great potential of using triage-based PDA systems in the mass gatherings. Overall, most of the subjects agreed with that the systems were easy to use and useful for the mass gatherings, and they were willing to accept the systems.