Changes in adrenal medullary and total cortical blood flow after hemorrhage have been described using radioactive microspheres. To assess changes in adrenal capsular and in intracortical adrenal blood flow, a method was used based on microscopic detection of non-radioactive microspheres. Injection of microspheres labelled with fluorescent dyes permitted multiple determinations of blood flow. Pentobarbital anesthetized dogs (n = 6) were prepared acutely with left ventricular and aortic catheters for injection and collection of microspheres, respectively. Adrenal denervation was done unilaterally by cutting the thoracic splanchnic nerve. Injections of 16-microns spheres were made prior to and immediately after 18 ml/kg hemorrhage done over 6 min. Dogs were killed with KCl and adrenals were removed, fixed and sectioned at 80 microns. Using fluorescence microscopy, microspheres were counted in the adrenal capsule, zona glomerulosa, inner cortex (zona facsiculata and reticularis), and the medulla. The majority (95%) of microspheres in the adrenal cortex were trapped in the zona glomerulosa, precluding an independent estimate of blood flow to the inner cortex. Thus, total cortical blood flow was determined by summing the number of 16-microns microspheres in the zona glomerulosa and inner cortex. Prior to hemorrhage, blood flow was greater in the capsule (5.4 +/- 1.6 ml/min/g) compared to the cortex (1.8 +/- 0.9 ml/min/g) and the medulla (2.9 +/- 1.8 ml/min/g). Splanchnicotomy did not change blood flow in the resting state. Following hemorrhage, in innervated glands, medullary blood flow increased to 8.6 +/- 3.1 ml/min/g, whereas blood flow to other zones was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS).