  We discuss the unitarity relation of the Aharonov-Bohm scattering amplitude
with the hope that it distinguishes between the differing treatments which
employ different incident waves. We find that the original Aharonov-Bohm
scattering amplitude satisfies the unitarity relation under the regularization
prescription whose theoretical foundation does not appear to be understood. On
the other hand, the amplitude obtained by Ruijsenaars who uses plane wave as
incident wave also satisfies the unitarity relation but in an unusual way.
