  Recent high resolution numerical simulations have suggested that the
interstellar atomic hydrogen clouds have a complex two-phase structure. Since
molecular clouds form through the contraction of HI gas, the question arises as
to whether this structure is maintained in the molecular phase or not. Here we
investigate whether the warm neutral atomic hydrogen (WNM) can exist in
molecular clouds. We calculate how far a piece of WNM which is not heated by
the UV photons could penetrate into the cloud, and find that in the absence of
any heating it is unlikely that large fraction of WNM survives inside high
pressure molecular clouds. We then consider two possible heating mechanisms,
namely dissipation of turbulent energy and dissipation of MHD waves propagating
in the WNM inside the cloud. We find that the second one is sufficient to allow
the existence of WNM inside a molecular cloud of size $\simeq$ 1 pc having
pressure equal to $\simeq 10 \times P_{\rm ISM}$. This result suggests the
possibility that channels of magnetised WMN may provide efficient energy
injection for sustaining internal turbulence which otherwise decays in a
crossing time.
