Though various parameters can be evaluated in ambulatory blood pressure monitoring, there is still a lack of reliable parameters for exact quantification of the early morning rise. Noninvasive ambulatory blood pressure monitoring (Space Labs 90207) was performed in 50 normotensive persons and in 52 patients with symptoms of orthostatic dysregulation. Twenty-two of the 52 patients showed normal and 19 showed sympathicotonic reactions in the orthostatic test by Thulesius. After smoothing the 24-h blood pressure profiles by Fourier analysis, the derivative was calculated from the profiles (differentiation) and the following parameters were determined: the beginning and the length of the early morning rise as well as time and point of the maximum rise. The maximum rise was compared to the difference between the nocturnal trough and the morning peak (absolute value) as well as to the percentage rise, where we found significant statistic correlations. Patients with sympathicotonic orthostatic dysregulation showed in comparison to the 50 normotensive persons a significantly lower (p < 0.05) maximum rise in blood pressure. Thus, Fourier analysis of 24-h blood pressure profiles allows determination of reliable parameters of the early morning rise in blood pressure and can be used for more precise differential diagnosis in patients with orthostatic dysregulation.