Acute renal failure was induced in heparinized rats by clamping the renal artery for 45 min. Ten minutes after recirculation the intrarenal blood flow distribution was measured. For this purpose labelled microspheres were injected together with 86‐Rb chloride. The microspheres were used for determination of cardiac output, total renal and cortical blood flow, and 86‐Rb for calculations of medullary blood flow. Total renal blood flow was reduced from 7.6 to 3.8 mlmin^‐1· g^‐1 and cortical blood flow was reduced from 11.7 to 7.0 ml · min^‐1· g^‐1. In the outer stripe of the medulla there was a reduction from 2.5 to 1.4 ml · min^‐1· g^‐1. In the inner stripe there was a more pronounced reduction from 1.8 to 0.2 ml · min^‐1· g^‐1 and in the inner zone from 0.8 to 0.1 ml · min^‐1· g^‐1. The marked reduction in the blood flow to the renal medulla after recirculation is suggestive for a medullary ischemia, which might be responsible for the characteristic dysfunctions in acute renal failure.