Six tests recommended for use in the diagnosis of cystic fibrosis (CF) have been compared in the same subjects. The tests were carried out on 165 normal persons, 64 known cases of CF, their 67 parents and 18 sibs. The tests measured sodium in fingernails by activation, sodium in saliva and chloride in saliva and in thermal and pilocarpine-induced sweat by means of ion-specific electrodes, and chloride in pilocarpine-sweat by the standard titrimetric method. The tests ranged in complexity from simple screening methods to individual clinical procedures. None of the simpler tests matched the standard pilocarpine method in diagnostic efficiency, whether they were used singly or in combination.