The glycoprotein vitronectin (also called S-protein, serum spreading factor, or epibolin) promotes spreading of a variety of cultured cells, inhibits the cytotoxicity of membrane attack complex C5b-9, and modulates thrombin-antithrombin III activity. We developed a strikingly simple method to purify vitronectin from human plasma by heparin affinity chromatography. Serum was obtained from plasma by adding calcium and then centrifuging. The heparin-binding activitiy of vitronectin in human serum was activated with 8 M urea. The activated vitronectin specifically bound to heparin-Sepharose in 8 M urea and was eluted with 0.5 M NaCl containing 8M urea. This procedure resulted in an approximately 250-fold purification of vitronectin with a 15-30% recovery; 3-6 mg of pure vitronectin were obtained from 100 ml human plasma within 2 days. The purified vitronectin preparations promoted spreading of BHK fibroblastic cells on substrates with a half-maximal activity at only 0.1 //g/ml. This new method is very simple, rapid, inexpensive, and flexible. It could probably be readily scaled up for commercial applications.