Hepatitis B surface antigen (HBsAg), was purified from plasma by affinity chromatography on matrix-bound sulphated carbohydrates such as heparin or dextran sulphate. Further purification by precipitation with polyethylene glycol (PEG) 6000 resulted in a highly purified HBsAg preparation. The overall recovery amounted to about 70% of the total antigen content of the starting plasma. Electron microscopic data revealed mainly 22 nm spherical particles accompanied by few or no filaments. The process is simple, rapid and lends itself readily to large-scale applications.