Two types of turbidity were found in parotid saliva from both cystic fibrosis (CF) patients and non-CF subjects. On cooling saliva, a rapidly forming, reversible, cold-dependent turbidity appeared in increasing amounts with decreasing temperature and increasing protein concentration. At 37 degrees, a slowly forming, stable turbidity appeared in increased amounts in parotid saliva samples containing increased amounts of calcium. The 2 degree centrifuged pellet consisted predominantly of protein, whereas the 37 degree pellet contained calcium, inorganic phosphate, and protein. The cold-dependent turbidity at 2 degrees was not inhibited by EDTA, but 37 degrees turbidity was dramatically inhibited. Urea and guanidine hydrochloride reduced 2 degree turbidity, and, to a lesser extent, inhibited 37 degree turbidity. The tendency towards higher levels of protein, amylase, and calcium in CF compared with child control parotid saliva (4, 6) causes a greater incidence and degree of turbidity formation in saliva of CF patients. In this paper only the nature of the turbidity has been investigated, not its relative occurrence in each group of subjects.