Staphylococcus aureus ATCC 49775 produces three proteins recognized by affinity-purified antibodies against the S component of Panton-Valentine leucocidin (LukS-PV) and two proteins recognized by affinity-purified antibodies against the F component of this toxin (LukF-PV). Purification of these proteins and cloning of the corresponding genes provided evidence for the presence of two loci. The first one, encoding Panton-Valentine leucocidin, consisted of two cotranscribed open reading frames, lukS-PV and lukF-PV, coding the class S and the class F components, respectively. The second one coded for a gamma-hemolysin and consisted of two transcription units, the first one encoding an HlgA-like protein, a class S component, and the second one encoding two cotranscribed open reading frames identical to HlgC and HlgB, class S and class F components, respectively, from gamma-hemolysin from the reference strain Smith 5R. It appears that the Panton-Valentine leucocidin from S. aureus ATCC 49775 (V8 strain) should not be confused with leucocidin from ATCC 27733 (another isolate of V8 strain), which had 95% identity with HlgC and HlgB from gamma-hemolysin. The cosecretion of these five proteins led to six possible synergistic combinations between F and S components. Two of these combinations (LukS-PV-LukF-PV and HlgA-LukF-PV) had dermonecrotic activity on rabbit skin, and all six were leukocytolytic on glass-adsorbed leukocytes. Only three were hemolytic on rabbit erythrocytes, the two gamma-hemolysin combinations and the combination LukF-PV-HlgA.