We examined the effects of mammalian tachykinins on human bronchial secretion in vitro using fucose as an endogenous marker for mucus. Substance P (SP, 10(-9)-10(-5) M) increased secretion in a dose-related manner and was more potent than neurokinin A or neurokinin B. The enkephalinase (endopeptidase 24.11) inhibitor phosphoramidon (10(-5) M) potentiated the effect of SP (10(-7) M). SP is a potent stimulant of secretion in human bronchi and enkephalinase may modulate its effects.