Abstract: A method of determining if a patient having cystic fibrosis has an increased risk of having or developing pulmonary exacerbations is described. The method includes determining the level of one or more metabolites associated with pulmonary exacerbations in a sweat sample from the patient, and characterizing the patient as having an increased risk of having or developing pulmonary exacerbations if one or more metabolites associated with pulmonary exacerbation are significantly different from a control value. A method of evaluating the response of a patient having pulmonary exacerbations to treatment is also described.