Corrosion replicas were made of the gill vasculature of the spiny dogfish shark (S. acanthias) and little skate (R. erinacea) by methylmethacrylate perfusion via the ventral or dorsal aorta at 2.0-5.3 kPa. After tissue maceration the replicas were examined by light and scanning electron microscopy. In both species 3 vascular pathways were found: (1) the major pathway subserving the respiratory function of the gill, consisting of the afferent filamental artery which feeds into a medial afferent sinus (MA) from which arise the prelamellar arterioles (AL) leading to the lamellae, the postlamellar arterioles and efferent filamental artery (EA); (2) a nutrient circulation arising from the EA, supplying oxygenated blood to the filamental tissue, and anastomosing with the interlamellar vessels (IL); (3) a collateral circulation consisting of ILs which drain through channels interdigitating with the ALs and which then form a collateral reticulum, beneath the water channel epithelium, with vessels from the adjacent filaments. In the dogfish, small prelamellar arteriovenous anastomoses (PA) connect the MAs to the ILs with the same frequency as the ALs. PAs have not been found in the skate, but the efferent nutrient circulation is much more extensively developed. Many similarities exist between the elasmobranchs and teleosts in regard to the microvascular organization of the gill.