A computer-assisted Medical Emergency Decisions and Assistance System (MEDAS) is proposed to improve the quality and effectiveness of medical care of the critically ill or injured patient. Guidelines for the management of immediately life-threatening problems are promptly available at any given stage. Interactive sequential diagnosis algorithm provides for the identification of multiple disorders in several body systems. The knowledge base for this algorithm consists of disorder patterns in a hierarchial structure that is based on physicians' subjective judgment as well as on statistical data, when such data is available. The system also provides recommendations for cost-effective information acquisition. Treatment protocols are formulated using a hierarchial -modular approach. Therapeutic directives and alternatives are keyed to the disorders and the clinician is alerted to the advantages, disadvantages and precautions of therapy. A permanent patient record is created which contains the observed findings, the diagnosis, the therapeutic actions and free format text. Special consideration is given to human factors related to man-machine interface. The use is given maximum flexibility in controlling the operational strategy. At any given stage, he may choose an operational strategy that ranges from full user control through mixed initiative to full system control. Likewise, the system is capable of explaining the reasoning process behind its decisions. The models are independent of the knowledge base, thereby permitting continuous up-date and expansions. The information structures lead themselves to compact storage and efficient computations. Feasibility of the undertaking has been demonstrated by simulation and by the use of patient cases on a retrospective basis. At its present stage of development, the medical content of the system contains 53 major disorders which are identified by 587 findings (i.e., "features"). The disorders are grouped into 10 major medical categories such as cardiovascular, respiratory, and neurological. A series of 35 treatment protocols have been developed including those which guide immediate resuscitation during cardiac arrest, anaphylaxis or exsanguination.