Blood flow in the hind-limb bones of 8 immature labrador dogs with unilateral knee joint tamponade at 75 percent of the mean arterial pressure was measured with 15-microns and 50-microns microspheres to determine whether or not arteriovenous shunting occurs in bone with venous congestion caused by increased outflow resistance. The intraosseous pressure was 43 percent of the mean arterial pressure in the experimental distal femoral epiphysis versus 14 percent in the control knee (P less than 0.001). No pressure changes were found in the distal femoral metaphysis. Regional blood flow with 15-microns microspheres decreased centrally in the distal femoral epiphysis and increased centrally in the proximal tibial epiphysis. Metaphyseal blood flow was largely unchanged. A net shift in the preferred embolization site of 50-microns microspheres relative to that of 15-microns microspheres from central to peripheral regions occurred within both juxtaarticular epiphyses, indicating arteriolar vasodilation, but the relation between the uptake of the two microsphere sizes was unchanged when the epiphyses and other bony flow compartments were viewed in toto. The result speaks against the hypothesis of arteriovenous shunting in intraosseous hypertension.