To further clarify the role of epidermal growth factor (EGF) in the physiology and pathophysiology of the ocular surface the effects of reflex tearing on concentrations of EGF in tear fluid were studied. Tear fluid samples were collected with glass capillaries before (basal samples, 59 eyes, 30 individuals) and during reflex tearing (stimulated samples, n = 212, 40 eyes, 20 individuals). The rate of tear fluid flow in the capillaries (TFFc) was measured. The concentrations of human EGF (hEGF) was determined by time-resolved immunofluorometric assay (TR-IFMA). The first basal samples contained higher concentrations of hEGF than the samples from the contralateral eyes (n = 28) collected thereafter (p less than 0.05). The basal samples from 40 eyes contained a significantly higher mean concentration of hEGF (8466 pg/ml) than did the stimulated samples (n = 212, 2763 pg/ml); p less than 0.001). The mean TFFc increased from 63 nl/s to 506 nl/s during reflex tearing (p less than 0.001) and the amount of hEGF released from 567 fg/s (n = 40) to 1400 fg/s (n = 212; p less than 0.001). Basal samples from females contained higher concentrations of hEGF than did those from males. The maintenance of the hEGF concentration at a certain level and the increased amount of hEGF released into the tear fluid during reflex tearing suggests continuous release of hEGF into tear fluid from the lacrimal gland.