We evaluated time-related blood pressure trends in the Tecumseh study participants, none of whom received antihypertensive treatment. At baseline the blood pressures were measured in the field clinic and by self measurement at home (twice daily for 7 days). After a mean of 3.2 +/- 0.42 years, the clinic and home pressure readings were repeated. Nine hundred forty-six subjects had clinic and home blood pressure readings at baseline. Of these 735 (380 men, 355 women; average age, 32 years) also completed the second examination. Blood pressure, morphometric data, and biochemical measures at the first examination were used as predictors of future clinic blood pressures. Five hundred ninety-six subjects were normotensive on both examinations (81%). Of 79 subjects (10.7%) with clinic hypertension (> 140 mg Hg systolic or 90 mm Hg diastolic) at baseline, 38 remained hypertensive ("sustained hypertension") and 41 became normotensive ("transient hypertension") after 3 years. Another 60 normotensives at baseline (10.4%) became hypertensive on second examination ("de novo hypertensives"; incidence; 8.1%). The home blood pressure readings on both examinations were reproducible. The three hypertensive groups had elevated home blood pressure, were overweight, had dyslipidemia, and higher insulin values. Only the home blood pressure proved predictive of subsequent blood pressure trends. A home blood pressure of 128 and 83 mm Hg or higher detected "sustained" hypertension with a 48% sensitivity and 93% specificity. Readings of 120 and 80 mm Hg or lower predicted future normotension with a 45% sensitivity and a 91% specificity. We conclude that self determination of the blood pressure at home is useful in the management of borderline hypertension. An algorithm for the management of these patients is proposed.