In this paper, we introduce a medical application of the Global Positioning System (GPS). For an asthmatic patient, he or she can carry a portable GPS device to prevent possible morbidity of asthma during his or her outdoor activities of daily livings. To reduce possible allergy asthma, the GPS-enable device continuously consults a remote server with sending user?s position to decide whether current ambient air quality will threaten user?s health. The server of the detecting system collects real-time data from the network of national air quality monitoring stations. For the response to a remote query, the server makes decision of warning messages according to a proposed asthma neural network model. The proposed system is hopeful for asthmatic patients.