To determine prevalence of diastolic arterial hypertension (DAH) in young individuals using different criteria. Secondly, to test the possible different blood pressure reactions to mental stress and hand grip in two groups: group A, a 'low blood pressure group', and group B, diastolic blood pressure 90 mmHg or greater in one interview and below these values in a second interview. SUBJECTS: A total of 1423 volunteer medical students was recruited at La Plata School of Medicine, average age 21 +/- 3 years. DESIGN: Systolic and diastolic blood pressure were measured three times on two different occasions separated by one week. With the values obtained, prevalence of arterial hypertension was determined according to the criteria suggested by The Joint National Committee 4 (JNC-4) and the World Health Organization (WHO), and to statistical bases. INTERVENTIONS: Mental stress and hand grip tests were performed by groups A and B. MAIN RESULTS: The prevalence of DAH when only the first determination of the first interview was considered was 14.7%, 6.7% (considering the WHO criterion) or 5% (using the statistical criterion). These values are reduced if repeated measurements are averaged. The greatest reduction was obtained when the JNC-4 criterion was used (1.6%). The reactivity of stressors did not show any relationship with the initial blood pressure of the subjects. CONCLUSIONS: In epidemiological studies, the differences among the criteria should be considered when analyzing blood pressure of populations. Stress tests (mental stress and hand grip) do not help in identifying differences between the groups studied.