Pertussis toxin is an exotoxin produced by the organism Bordetella pertussis. The toxin binds to receptors on the eukaryotic cell surface. After introduction into the eukaryotic cell, the toxin is activated by ATP and subsequently ADP-ribosylates a family of GTP-binding regulatory proteins interrupting signal transduction within the cell. We have examined the location of several critical sites on the toxin molecule. These sites include the receptor binding site and the ATP binding site. The B oligomer of the toxin was found to contain at least two sites capable of binding glycoproteins suggesting that the B oligomer may have more than one eukaryotic cell receptor binding site. ATP was also shown to bind to a site on the B oligomer. These results indicate that the B oligomer contains several sites necessary for toxin action.