The effect of intrarenal artery injection of bradykinin (BK, 5.0 μg/kg) on multi- and single-unit recordings of afferent renal nerve activity (ARNA) was examined in anesthetized 48 rabbits. The results obtained are as follows. (1) There were two phases of increase in ARNA following intrarenal BK. The early phase occurred immediately while the delayed phase made its appearance about 7 min later. The degree of increase in ARNA of the delayed phase induced by intrarenal BK was more prominent than that in the early phase. BP was actually unaltered following intrarenal BK. (2) By pretreatment with indomethacin (Indo, 5.0 mg/kg), the delayed phase of increase in ARNA induced by intrarenal BK was attenuated, while the early phase was not affected. (3) Pretreatment with L-NAME (30 mg/kg) led the delayed phase to be blocked completely while the early phase was partially decreased. From the above-mentioned observations, it is concluded that intrarenal BK induces a significant increase in ARNA in two phases. The early phase may be due to the direct action of BK and partially due to the NO action, while the delayed phase may be attributed to the action of released prostaglandin and NO as a result of intrarenal BK.