Work stress has repeatedly been associated with an increased risk for cardiovascular disease. This study tested whether this relationship could be explained by exaggerated cardiovascular reactivity to work or impaired recovery in leisure time. Vagal tone was assessed as a possible determinant of these work stress effects. Participants included 109 male white-collar workers (age, 47.2+/-5. 3) who were monitored on 2 workdays and 1 nonworkday for ambulatory blood pressure, heart rate, and heart rate variability. Chronic work stress was defined according to Siegrist's model as (1) high imbalance, a combination of high effort and low reward at work, or (2) high overcommitment, an exhaustive work-related coping style indexing the inability to unwind. All findings were adjusted for possible differences in posture and physical activity between the work stress groups. High imbalance was associated with a higher heart rate during work and directly after work, a higher systolic blood pressure during work and leisure time, and a lower 24-hour vagal tone on all 3 measurement days. Overcommitment was not associated with an unfavorable ambulatory profile. Logistic regression analysis revealed that heart rate [odds ratio 1-SD increase 1.95 (95% CI, 1.02 to 3.77)] and vagal tone [odds ratio 1-SD decrease 2.67 (95% CI, 1.24 to 5.75)] were independently associated with incident mild hypertension. Surprisingly, the values during sleep were more predictive for mild hypertension than the values during work. The results from the present study suggest that the detrimental effects of work stress are partly mediated by increased heart rate reactivity to a stressful workday, an increase in systolic blood pressure level, and lower vagal tone.