  We present a study of gas-phase H2O and CO2 toward a sample of 14 massive
protostars with the Short Wavelength Spectrometer (SWS) on board the Infrared
Space Observatory (ISO). Modeling of the H2O spectra using a homogeneous model
with a constant excitation temperature T_ex shows that the H2O abundances
increase with temperature, up to a few times 10^-5 with respect to H2 for the
hottest sources (T_ex ~500 K). This is still a factor of 10 lower than the H2O
ice abundances observed toward cold sources in which evaporation is not
significant (Keane et al. 2001). Gas-phase CO2 is not abundant in our sources.
The abundances are nearly constant for T_ex>~100 K at a value of a few times
10^-7, much lower than the solid-state abundances of ~1--3 times 10^-6
(Gerakines et al. 1999). For both H2O and CO2 the gas/solid ratio increases
with temperature, but the increase is much stronger for H2O than for CO2,
suggesting a different type of chemistry. In addition to the homogeneous
models, a power law model has been developed for one of our sources, based on
the physical structure of this region as determined from submillimeter data by
van der Tak et al. (1999). The resulting H2O model spectrum gives a good fit to
the data.
