Quality assurance has become an important issue in emergency medicine. At present, no prospective studies are available that quantify the efficacy of interventions performed by emergency doctors. The development and implementation of a rapid, yet simple scoring system, allowing preclinical assessment of all emergency medicine patients, is required. Once the scoring system is implemented, evaluation of the prehospital intervention, based upon objective parameters, is possible. METHODS. The Mainz Emergency Evaluation Score (MEES) is based on seven parameters: level of consciousness, heart rate, heart rhythm, arterial blood pressure, respiratory rate, partial arterial oxygen saturation and pain. A coded value is assigned to each parameter, with the normal physiological condition securing a score of 4, while a life-threatening condition receives a value of 1. For the parameter of pain there is no life-threatening condition, so the lowest value allowed is 2 (Table 2). Addition of the respective values from the seven parameters yields the MEES value, which objectively reflects the patients' condition (minimum = 8, maximum = 28). Comparing the MEES value before (MEES1) and after the intervention (MEES2) allows an objective evaluation of the efficacy of the preclinical care (delta-MEES = MEES2-MEES1). A difference of > or = +2 is considered an improvement, +1, +/- 0, -1 are rated as unchanged and < or = -2 is considered a deterioration in the patients condition. For more detailed evaluation the patients were allocated to 16 diagnosis groups (Table 3). Statistical evaluation utilized analysis of variance, the rank sum test (Wilcoxon) and the correlation coefficient (Kendall-Tau). RESULTS. In 356 patients the condition of 187 (52%) patients improved during the preclinical treatment; the condition of 156 (44%) patients did not change. In 13 patients (3%) the condition became worse (Table 5, Fig. 2). Allocation to 16 diagnosis groups revealed that the improvement in the patient's condition depended on the underlying disease (Table 3); the disease-specific parameter improved in all cases (Table 7). CONCLUSIONS. With the MEES score one can assess the patient's prehospital condition and monitor any improvement or deterioration during subsequent intervention and transport. The MEES was found to be easy to use, reliable and not an additional burden to emergency doctors. The MEES provides a means of assessing the efficacy of preclinical treatment. This score does not allow outcome prediction; this requires the inclusion of hospital data. Assessment of the efficacy of prehospital intervention is an important first step in the inclusion of quality assurance in emergency medical systems.