Isoelectric focusing of purified staphylococcal enterotoxin C2 revealed the presence of as many as eight immunologically identical protein fractions in a pH 5–8 ampholyte system with pI (isoelectric point) values of 7.35, 6.95, 6.75, 6.55, 6.20, 5.95, 5.70, and 5.50, respectively. In refocusing experiments, fractions of the toxin were found to arise by conversion from a more basic protein fraction.