Griffiths' point is defined as the site of (a) communication of the ascending left colic artery with the marginal artery of Drummond, and (b) anastomotic bridging between the right and left terminal branches of the ascending left colic artery at the splenic flexure of the colon. It is upon this critical point at the splenic flexure that collateral circulation between the superior mesenteric artery and the marginal artery branch of the inferior mesenteric artery supplying the descending colon is dependent. Analysis of arteriographic studies shows that anastomosis at Griffiths' point is present in 48%, poor or tenuous in nine percent, and absent in 43%. This critical point is of significance in occlusive vascular impairment of the left colon, both in spontaneous instances and following surgical ligation of the inferior mesenteric artery, and in "nonocclusive" ischemic colitis. Its relationship to arteriosclerotic stenoses and low flow states is discussed. Individuals with absence of dependable anastomoses at Griffiths' point at the splenic flexure may be particularly vulnerable to low perfusion states and develop the syndrome of ischemic colitis. Complete arteriographic evaluation is necessary in ischemia of the colon. This includes particularly assessment of atherosclerotic changes at or near the ostia of the major visceral arteries and the vascular arrangement at Griffiths' point.