Objective. To examine the extent to which ambulatory blood pressure was predicted by blood pressure levels exhibited during talking segments of a laboratory protocol and by resting blood pressures in male and female adolescents from three ethnic groups: African, European and Hispanic Americans. Design. This was a laboratory-field study incorporating an experimental study of reactivity of blood pressure during a laboratory protocol and an observational study of 24 h ambulatory blood pressure (ABP) monitoring. Methods. Resting blood pressure, reactivity of blood pressure, 24 h ABP, and activity, height, and maturation of a multi-ethnic sample of 373 male and female adolescents aged 11-16 years were measured. A mixed-effects model for repeated measures was the statistical approach, with systolic and diastolic blood pressures as separate, dependent variables. Results. Percentiles of ABP by sex, ethnic group, and height are presented. High and mixed blood pressure reactors in the laboratory had higher levels of 24 h ABP and higher levels of blood pressure load during the daytime. African Americans had higher ABP than did European and Hispanic Americans. Conclusions. Blood pressure measured during laboratory tasks that require talking might be useful as a screening device to identify adolescents with high blood pressures. Further study will be necessary in order to quantify the sensitivity of the laboratory protocol as an indicator of high blood pressure compared with casual measurement of blood pressures. If laboratory patterns of blood pressure could be used to predict which individuals have high levels of blood pressure during the course of daily activities, the laboratory protocol would be a useful screening tool, identifying high-risk individuals.