 The study is an open-labeled parallel prospective trial comparing the effects of doxazosin 2-8 mgday on 24-h blood pressure and autonomic nervous activity. Hypertensive patients with non-insulin-dependent diabetic nephropathy, patients with essential hypertension, patients with diabetes mellitus and patients with chronic nephropathy undergo ambulatory blood pressure monitoring before and after treatment with doxazosin. Simultaneously, spectral analysis is performed to calculate the high frequency components as a marker of parasympathetic nervous activity, and the low frequency componentshigh frequency components ratios as an index of the sympathovagal balance. 