Stress is an emergent occupational problem in modern societies. Among workers, medical practitioners are particularly exposed. However, data objectifying stress levels during work time are scarce. The aim of this study was to establish diurnal salivary cortisol levels in a highly stressful work environment, the medical dispatch center of an emergency care unit.Eight emergency medical dispatchers agreed to be sampled every 2 hours from 9 AM to 7 PM during a usual day of work. Eight matched control subjects sampled during their leisure time were used as a control group.Whatever the time of the day, emergency medical dispatchers showed significantly increased cortisol levels during their work time compared with levels found in the control group. There was a significant difference in the amount of daytime cortisol secretion between control subjects and emergency medical dispatchers (0.345 nmol/L; 95% confidence interval [CI] 0.04 to 0.93 nmol/L), with a mean daytime augmentation of 22.8% in emergency medical dispatchers compared with that in control subjects. In addition, among emergency medical dispatchers, the subjective perception of emotional stress was positively correlated with total cortisol concentrations per day (r =0.78; 95% CI 0.39 to 1).Our data show that work tasks of emergency medical dispatchers led to a hypersecretion of cortisol. Because the damaging effects of persistent cortisol increases on health and cognitive functions are well recognized in human beings, it seems necessary to rapidly identify stressful work situations and targets for organizational improvements to minimize stress in these situations.