The rabbit dorsal flank flap is useful for microvascular and flap research. Twenty-four rabbits were studied to assess the constancy and caliber of the blood supply to this flap. The sizes of the main pedicle vessels were measured in live animals. Lead oxide arteriograms were performed to assess the vascular pattern and territories. The pattern of supply was regular in over 85 percent (21) of the animals-a twin angiosome system, each territory being supplied from opposite ends of the flap and meeting in the central portion with choke anastamoses. Both proximal and distal territories were constantly supplied by a single large perforating vessel, the thoracodorsal vessels supplying a median of 59 percent of the flap, and the deep circumflex iliac vessels 41 percent. In three animals, a body wall perforator added a third flap territory, supplying a variable area ranging from 7 to 18 percent. The sizes of the vessels in each vascular pedicle were suitable for microvascular anastamosis, with the thoracodorsal vessels constantly larger (median size artery: 0.9 mm; vein: 1.2 mm) than the deep circumflex iliac vessels (median size artery: 0.7 mm; vein: 1.0 mm).