  If the Standard Model of particle interactions is extended to include a
second scalar doublet $[H^{+},(H^{0}+iA^{0})/\sqrt{2}]$, which is odd under an
unbroken Z_{2} discrete symmetry, it may be called the $dark$ scalar doublet,
because its lightest neutral member, say H^{0}, is one posssible component for
the dark matter of the Universe. We discuss the general phenomenology of the
four particles of this doublet, without assuming that H^{0} is the dominant
source of dark matter. We also consider the impact of this $dark$ scalar
doublet on the phenomenology of the SM Higgs boson h.
