An effective concentration of alpha-toxin from Staphylococcus aureus Wood 46, directly from the culture supernatant, could be achieved by adsorption on digitonin-sepharose and elution with 3 mol/l sodium thiocyanate (NaSCN). The toxin was further purified by gelchromatography. The purified product yielded 1 single protein band upon SDS-polyacrylamide electrophoresis. It was nonhemolytic, but reacted with anti-alpha-toxin under complement fixation. Dialysis against 0.14 mol/l NaCl with hydrophobic amino acids partially reactivated the alpha-hemolytic activity of the toxin. Ultracentrifugal analysis yielded sedimentation coefficients for the purified toxin of approximately 3,7 S when dissolved in 3 mol/l NaSCN and of about 12 S after dialysis against 0.14 mol/l NaCl (Table 1). The spontaneous oligomerization of the alpha-toxin during dialysis against 0.14 mol/l NaCl possibly resulted from a change in configuration induced by its adsorption to digitonin-sepharose.