Intermittent patchy ischemia in the renal cortex has been observed in dogs during traumatic shock. In search of a model for further studies of this phenomenon in anesthetized rats, we induced tourniquet shock by bilateral hindlimb occlusion for 3 1/2 h, and burn shock by scalding the hind 50% of body surface for 30 sec in 90 degrees C water. Local cortical blood flow (RCF) was repeatedly measured by the H2-washout technique. After releasing the tourniquets, mean arterial pressure (AP) and RCF decreased by 44 and 68% whereas hematocrit (Hct) rose to 66 vol%. Only two episodes of local ischemia were observed. After scalding, Hct first fell to 49 vol%, probably due to hemolysis, but rose toward 54 vol% in the next 2 h. Following an initial drop to 99 mmHg, AP was relatively well maintained throughout the experiment. The RCF fell to 53% of control within 15 min with a further decrease to 40% during the next 2 h. The cortical vascular resistance was increased by 89%. Increased local flow heterogeneity and episodes of patchy intermittent ischemia were observed in six out of eight rats. During the second hour postburn, 21% of the washout curves showed abrupt shifts of washout rates, indicating local cortical ischemia. The burn shock model seems well suited for studies of the mechanisms causing intermittent local ischemia.