8 sweat tests were performed in each subject at a proper interval time and under different combination of the inquired conditions. The study design permitted to measure chloride intra-individual variability and to explore intra-individual variability in regard to sex, salt content diet, pre/post pubertal age, type of diagnosis (classic CF, CFTR-related disorders, healthy condition). Results underlined high intra-individual variability of chloride concentrations, being this variability more elevated in healthy subjects (however always in the normality range) and in CFTR-related disorders than in classic CF patients. Salt content diet was studied in healthy subjects and in CFTR-related disorders and seemed no to be influent on chloride level. In all the groups no correlation was seen neither in regard of pre/post pubertal age nor in regard to menstrual cycle phase. In CF patients group chloride level resulted significantly lower in the autumn-winter season than in spring-summer, even if it never dropped below the pathologic value. This result may be related to different hydration conditions of CF patient in different periods of the year. Further studies based on wider samples of patients could give interesting insights on sweat test results variability.