This study was designed to compare the 24-h blood pressure profile of young physicians during on-call days with those obtained during a normal day, and to explore the factors related to blood pressure reactivity in a stress situation. The study was a self-comparison study in two environments (on-call and at home). The study population was 100 physicians, staff, and residents working in the emergency room. A previously validated ambulatory, automated, auscultatory blood pressure (BP) monitoring device (A&D Takeda 2420) was used. BP measurements were programmed to be taken every 15 min and three time periods were considered for analysis: the whole day, awake, and sleep periods. Systolic and diastolic BP behavior were described by their average and distributions. Within each considered phase (on-call, at home) the pressor response was defined as the difference in average blood pressure. Being on-call modified both systolic and diastolic ambulatory BP profiles. Both average BP values and BP load were significantly higher when subjects were on-call. Systolic blood pressure increased in 83% of subjects and 40% displayed a significant pressor response of 10 mm Hg or more. For diastolic blood pressure some increase was observed in 93% of subjects, and a significant pressor response of 10 mm Hg or greater in 23% of them. Age, sex, personality, and tobacco consumption were not associated with the pressor response. Familial history of hypertension and professional status were the most important determinants of the pressor response.