An in vitro process for the detection and early detection of neurodegenerative diseases, for determination of the severity, and to evaluate the progression of and render a prognoses of neurogenerative diseases, in a patient suffering from a subjectively or objectively detectable cognitive impairment, by determining the concentration of an analyte selected from natriuretic peptides, in particular ANP, and, if necessary, BNP and/or CNP in a biological fluid of the patient, whereby the determination of the analyte is performed directly and/or indirectly as the determination of a relevant co-peptide generated from a mutual propeptide, and is based upon the measured concentration of the determined analyte thus making it possible to form conclusions about a neurodegenerative disease or an early form typical of such a disease or the course of the disease and/or the success of the efforts to relieve or prevent the disease.