Current behavioral medicine research focuses on the role of psychological factors in the development of essential hypertension. Implicit in the rationale for much of this psychophysiological research are assumptions that individuals differ in characteristic blood pressure (BP) reactivity to stressful situations at home and work, and that individual differences in BP reactivity to challenging, emotion-eliciting, laboratory tasks reflect these differences. The three (3) studies proposed here will test these assumptions by comparing individual differences in BP reactivity during emotion-eliciting laboratory tasks and 24-hour ambulatory BP variability. The first two studies compare groups with either high or low trait-anger, high or low trait-anxiety, positive or negative family history of hypertension, or borderline or normotensive casual BP levels. If the assumptions above are valid, then the groups with high trait-anger, high trait-anxiety, positive family history of hypertension, or borderline casual BP levels should show both greater BP reactivity to the laboratory tasks and higher daytime ambulatory BP levels, compared to groups without these characteristics. The third study compares individual differences in BP reactivity during the laboratory tasks with ambulatory BP responses during an acute (public speaking) potentially stressful life event. According to the assumptions above, individuals with the greatest laboratory BP reactivity should show the largest increases in ambulatory BP during the stressful life event. The results of these studies should provide support needed for assumptions underlying important psychophysiological research into the determinants of essential hypertension.