We investigated whether body mass index and blood pressure have an additive influence on the carotid intima-media thickness (IMT). In 27 patients treated for hypertension (47.2 +/- 8.7 years) and 23 normotensive subjects (44.1 +/- 8.1 years), 24-h recording of blood pressure was performed. The carotid IMT was determined by ultrasonography and baroreflex sensitivity by a spectral method from 5-min recordings of blood pressure. Significant differences between hypertensive and normotensive subjects were observed for carotid IMT (0.60 +/- 0.08 vs. 0.51 +/- 0.07 mm; p < 0.001) and baroreflex sensitivity (3.5 +/- 1.8 vs. 5.6 +/- 2.1 ms/mm Hg; p < 0.001). Hierarchical multiple regression analysis (p < 0.01) showed that carotid IMT was positively correlated with age (p < 0.001) and body mass index (p < 0.05) in normotensive subjects. The increased carotid IMT in hypertensive patients was not additively influenced by either age or body mass index. Baroreflex sensitivity decreased with age (p<0.01) and with carotid IMT (p<0.05) in normotensive subjects only. Multiregression analysis showed that an additive influence of age and body mass index on the development of carotid IMT is essential only in normotensive subjects. In hypertensive subjects the influence of blood pressure predominates, as documented by a comparison of the carotid IMT between hypertensive and normotensive subjects.