Radio  observations of warm molecular clouds provide a partial picture
of  their  molecular  content.  Some  molecules  are  observed from the
emission of only one rotational line, other from a few, and most of the
molecules  that  probably  exist  in  these  clouds are never observed.
However,  mid  and  far  IR  spectroscopy  with  ISO can provide a full
description  of the molecular content of the most conspicuous molecular
clouds of our galaxy for a moderate cost in observing time.
 We propose to carry out a full resolution SWS grating survey between 4
and  45  um  in  some  prominent  molecular  clouds  as SgrA, W51-IRS1,
NGC6334N,    Orion-IRC2,  M17,  etc  (see  Table  1). In order to fully
explore  the  infrared  spectrum  of  these conspicuous clouds, we also
propose  to  carry  out  a LWS fast scanning FP survey in some of these
sources.  Because  of  the  high kinetic temperature of these clouds we
expect to see all the lines in emission for wavelengths above 80-100um.
 In  addition  to the molecular content of these warm molecular clouds,
the  cold  dark  clouds in their line of sight will also produce strong
absorptions.  They  will  be  easily  recognized from the low number of
ro-vibrational  lines  that will appear and in the case of SgrA because
the large velocity shift between it and the local cold dark clouds.
The proposed observations will provide a full database of the molecular
content of warm molecular clouds and of the local cold dark clouds. The
molecular  abundances  and  the  physical conditions of the gas will be
accurately  derived.  Hence,  these observations will provide an unique
check  of  our current understanding of the chemistry in these objects.
In  addition  to  the  normal  and suspected molecular bands that these
clouds  will present, many new molecules will be seen. This survey will
also provide a detailed database the next two decades for spectroscopic
and physical studies of warm molecular cloud. We stress that one of the
last  unexplored  windows  of  the  electromagnetic  spectrum  of these
prototypical clouds will be finally open by the ISO spectrometers.