Staphylococcus aureus is an important opportunistic pathogen. It produces a variety of extracellular proteins, which may play important roles in infections by this bacterium. Staphylococcal alpha-toxin is a pore-forming 33-kDa polypeptide. In the first part of this article, we will refer to the roles of cell membranes in the pore formation by alpha-toxin as well as the molecular dissection of alpha-toxin for understanding its pore-forming nature. Staphylococcal gamma-hemolysin and leukocidin are bi-component cytolysins, which have different cell specificities towards erythrocytes and leukocytes, respectively. We have found that these bi-component cytolysins share a common component. In the second part of this article, we will refer to the current status of knowledge of molecular cloning of the genes coding for gamma-hemolysin and leukocidin, molecular domains of the toxins which decide the cell specificities, and mode of action of these bi-component toxins.