The physiological variations of fibrinolytic activity (FA) in saliva were investigated in a population of 149 healthy volunteers including 12 pregnant women. An increase in FA could be observed with increasing age. Marked variations were observed during daytime with a peak value early in the morning. Higher FA values were observed in males as compared with females in the 20-39 yr age group. A clear decrease in FA was observed during pregnancy. A significant correlation existed between FA and suspended epithelial cell concentration, which seemed responsible for most of the physiological FA variations. It was concluded that age, sex, pregnancy, and the time of the day are important for salivary FA and should be taken into account in any study on salivary FA related to physiological or pathological processes.