Background Our aim was to assess psychomental stress and strain among dispatchers in fire departments, particularly during emergency instructions by phone and to evaluate their work ability. Methods 27 dispatchers and 20 controls were examined. In a protocol, participants recorded 1. phone instructions causing mental stress (event) 2. working time without phone instructions (non-event) 3. breaks. Continuous heart rate (variability), urine catecholamine, salivary cortisol and lymphocytes were measured. To assess the job-related burden, the Work Ability Index (WAI) was applied. Results Dispatchers demonstrated significantly higher heart rates and reduced standard deviation of all NN (heartbeat-to-heartbeat) intervals (SDNN) than the controls in all phases. WAI of dispatchers was significantly lower than that of the controls. Within the dispatchers, there was a significantly higher rate of inability to work during the past year. Conclusions The increased heart rate and reduced SDNN of examined dispatchers indicate chronic stress effects as a possible preliminary stage of a health disorder. In respect of the reduced work ability among dispatchers preventive measures are required to reduce the stress situation during their job-performance.