The sweat test, a quantitative measurement of chloride in sweat, remains a key laboratory test to support the diagnosis of cystic fibrosis. However, because of its delicate execution, sweat test result should be interpreted with biological, clinical and genetic arguments. The following guidelines which we propose, were established in order to harmonize the practices of the sweat test. They are elaborated in a consensual way by biologists from cystic fibrosis reference centers and/or from the working group "Sweat Testing" of the National College of Biochemistry Hospital praticiens, according to the current state of knowledge on the subject, the experiment of the biologists and the recommendations established in the United States and in the United Kingdom.