Alpha-toxin, also known as alpha-hemolysin (Hla), is the major cytotoxic agent released by bacterium Staphylococcus aureus and the first identified member of the pore forming beta-barrel toxin family.

This structure allows the toxin to perform its major function, development of pores in the cellular membrane, eventually causing cell death.

Alpha-toxin has been shown to play a role in pathogenesis of disease, as hly knockout strains show reductions in invasiveness and virulence.

Incubation of T-cells, monocytes, and peripheral blood lymphocytes with either purified alpha-toxin or S. aureus cell lysate resulted in the induction of apoptosis via the intrinsic death pathway.

In 1996 it was first shown that single-stranded nucleic acids can be detected by electrophysiology measurements as they translocate through an alpha-hemolysin pore embedded in a lipid bilayer.