The effect of anoxia on cerebral blood velocity (CBV) on the dorsal surface of telencephalon was examined in the leopard frog, Rana pipiens, using a stereomicroscope. During exposure to anoxia, a transient 228% increase in CBV velocity was seen after 20 min, but CBV fell back to basal values after a further 20 min of anoxia. Topical application of 50 microM adenosine during normoxia caused a 52% increase in CBV, while 250 microM adenosine caused no further increase. At both concentrations, the effect was completely inhibited by the adenosine receptor blocker aminophylline (250 microM). Superfusing the brain with aminophylline during anoxia did not affect the anoxia-induced increase in CBV. We conclude that adenosine can stimulate CBV in R. pipiens. However, unlike in other anoxia-tolerant animals, adenosine seems not to be a main mediator of the anoxia induced increase in CBV in the frog.