An operational threshold for making clinical decision on the basis of ambulatory blood pressure monitoring must be defined. This requires that the relationship between the ambulatory pressure and the incidence of cardiovascular complications be clarified beyond present understanding. Preliminary cut-off points for ambulatory monitoring were derived by averaging the 95th percentiles of the ambulatory blood pressure measurements for the normotensive subjects enrolled in various large-scale studies. According to this approach, the upper limits of normotension, calculated by rounding downwards, would be 130/80mmHg for the 24h blood pressure and 135/85 and 120/70mmHg for the daytime and night-time blood pressures. Abnormality, obtained by rounding upwards, would be blood pressure levels exceeding 135/85, 140/90 and 125/75mmHg, respectively.