Cellular localization of the B1 receptor mRNA in the human kidney was identified by in situ hybridization histochemistry using digoxigenin-labeled riboprobe. With the antisense riboprobe, the B1 receptor mRNA was found mostly in the parietal layer of Bowman's capsule and the thin segment of Henle's loop. The renal carcinoma cells were stained with the B1 receptor riboprobe. These results showed the cellular localization of human renal B1 receptor mRNA and revealed sites of bradykinin action in regulating renal function under normal and pathological conditions.