A new method was developed for the purification of type beta transforming growth factor from human platelets. This method is a three-step procedure including gel filtration, weak cation exchange HPLC and reverse phase HPLC. All steps are carried out at low pH using exclusively volatile acidic buffer solutions. The sterile conditions and easy removal of salt by lyophilization facilitate the quantification of the growth factor in biological assays. Based on immunological characterization the purified acid-stable, highly basic transforming growth factor beta is the beta 1 form. Using the present method pure platelet TGF beta 1 is obtained in very high yield. 40 units of outdated human platelets yield 800 micrograms pure TGF beta 1, which is about a 10-20 fold higher yield than reported for other purification procedures.