1. An in vitro method of identifying normal and abnormal diurnal cortisol secretion patterns from human saliva samples, wherein first and second saliva samples are taken from one human individual at first and second predefined times during the same day, a first cortisol concentration is determined in the first saliva sample, and a second cortisol concentration is determined in the second saliva sample, characterized by the steps of providing first and second variables (cort_conc_slope, cort_conc_mean); assigning values to the first and second variables which are associated with the determined first and second cortisol concentrations; providing a set of predefined constants (alpha, beta, gamma) for each variable; calculating, for each variable, a first fuzzy logic index (high_ind) to represent a degree to which the variable has a high value in relation to the predefined constants; calculating, for each variable, a second fuzzy logic index (low_ind) to represent a degree to which the variable has a low value in relation to the predefined constants; matching different combinations of the first and second fuzzy logic indices, as calculated for the first and second variables, with predetermined definitions of a normal diurnal cortisol secretion pattern and at least one abnormal diurnal cortisol secretion pattern; and selecting the definition where the best correspondence occurs.