On the basis of the heparin-like effect of phosphotungstate (PTA), we have shown that it is useful for the purification of hepatitis-B virus surface antigen (HBsAg) using heparin-Sepharose affinity chromatography. HBsAg was eluted with 0.2-0.6 M NaCl. HBsAg was also eluted with PTA at approximately 1 mM, and the HBsAg fraction thus obtained contained fewer impurities than the corresponding fraction eluted with NaCl. Moreover, PTA yielded HBsAg and hepatitis-B virus e-antigen simultaneously. PTA may specifically reduce the affinity of HBsAg for heparin as well as simply competing with heparin for an anion-binding site of HBsAg. Residual PTA in the eluate was easily decomposed by alkalization, which was useful for subsequent studies.