Abstract
The Stokes radius of unpurified hepatitis B antigen (HBsAg) was determined by chromatography on a carefully calibrated Sepharose 4B column. A value of 14.2 nm was found by this procedure, contrasting with a published value of 11 nm for purified, pepsin-treated HBsAg. Chromatography at pH 3 appeared to reduce the Stokes radius of HBsAg to 11 nm. Evidence is presented to show that serum proteins adsorbed to HBsAg can be removed with pepsin or acid.