Fibrin thrombi due to slow intravascular coagulation appear simultaneously in rat kidney, liver, lung, and spleen, although the kidney is the only organ to show fibrin by light microscopy. The strands of fibrin are frequently associated with aggregation and viscous metamorphosis of platelets, particularly in the lungs. Some fibrin is eliminated by the reticuloendothelial system and through damaged glomeruli, but the major mechanism of removal is intravascular dissolution. Ischemic changes secondary to thrombosis are more prominent in glomerular capillaries than in other tissues. The morphologic observations are discussed in relation to "preparation" for the generalized Shwartzman reaction.