Phosphatidylinositol-specific phospholipase C (PIPLC), an enzyme that can specifically release phophatidylinositol-linked proteins from host cells, is one of the extracellular enzymes produced by Staphylococcus aureus. To investigate whether PIPLC might be a virulence factor, we assessed PIPLC production by S. aureus strains that had been isolated from healthy carriers and from infected patients with or without toxic shock syndrome. Although none of five vaginal isolates from healthy women was a PIPLC produced, only 10 of 32 selected pathogenic strains that caused significant infections or toxic shock syndrome elaborated PIPLC enzyme activity. Seven of 24 toxic-shock-associated strains, compared with 3 of 8 non-toxic-shock-associated strains, were positive for PIPLC. The majority of strains that produced PIPLC were negative for toxic shock syndrome toxin 1 (P < 0.05); this association between PIPLC production and strains negative for toxic shock syndrome toxin 1 was even stronger among strains isolated only from patients with toxic shock syndrome (P < 0.01). Among all 32 pathogenic isolates, PIPLC-producing S. aureus strains were isolated from four of four patients developing adult respiratory distress syndrome and four of five patients with disseminated intravascular coagulation, suggesting a significant association between PIPLC production and adult respiratory distress syndrome and/or disseminated intravascular coagulation (P < 0.002). On the basis of these results, we propose that PIPLC is a virulence factor of S. aureus and is implicated in the development of adult respiratory distress syndrome and disseminated intravascular coagulation.