We are studying the structures of bacterial toxins that form ion channels and catalyze macromolecule transport across membranes. For example, the crystal structure of the Staphylococcus aureus α-hemolysin (α-HL) channel in its functional state was confirmed using neutron reflectometry (NR) with the protein reconstituted in membranes tethered to a solid support. This method, which provides high-resolution structural information, could test putative structures of the Bacillus anthracis Protective Antigen 63 (PA63) channel, locate where B. anthracis Lethal Factor and Edema Factor toxins (LF and EF, respectively) bind to it, and determine how small molecules can inhibit the interaction of LF and EF with the channel. We report here the solution structures of PA63 and its precursor PA83 obtained with small angle neutron scattering. At near neutral pH, PA83 is a monomer and PA63 a heptamer. The latter is compared to two markedly different cryo-electron microscopy structures. We also show that although the α-HL and PA63 channels have similar structural features, unlike α-HL, PA63 channel formation in lipid bilayer membranes ceases within minutes of protein addition, which currently precludes the use of NR for elucidating the interactions between PA63, LF, EF, and putative therapeutic agents.