The experiments based on morphologic examination and clearance kinetics clearly indicate that the kidney is the predominant site of toxin localization after intravenous injection of Staphylococcus enterotoxin B. Experiments show that the majority of the toxin found in the kidneys of both rat and monkey is located in the proximal convoluted tubules. Evidence has been advanced to substantiate the hypothesis that toxin gains access to the renal tubules by glomerular filtration and tubular reabsorption. Having gained access to proximal tubules, the toxin remains there for several hours. The possibility that SEB recycles through the kidney by being transported across renal cells and returned to the circulation is not excluded. However, significant redistribution of labeled toxin from the kidney to other sites did not appear to occur despite the increased fluorescence noted with time in liver Kupffer cells as well as a slight increase in radioactivity labeled toxin in the lung. Of considerable interest is the fact that the alternative site to toxin localization in the kidney is the liver and that at no time could evidence be obtained for cerebral localization of the toxin.