This study was undertaken to test the effect of static, empty-mouth clenching on blood pressure levels in normotensive and hypertensive subjects. Blood pressures were measured before, during, and after one minute of empth-mouth static (isometric) clenching in 41 normotensive (group A) and 22 hypertensive subjects (group C). An additional group of 13 normotensive subjects (group B) were examined for elevations in blood pressure before, during, and after 30 seconds of clenching. Subjects in group A showed a clenching-related increase in mean arterial blood pressure of 5.5 mm Hg (P less than .001); in group C, there was an increase of 4.6 mm Hg (P less than .001); and in group B, there was an increase of 3.2 mm Hg (P less than .05). The results emphasize the relationship between isolated dental treatment and systemic health.