  We have investigated the role of the stress-induced by the presence of the
substrate in thin films of colossal magnetoresistive manganites on structural,
resistive and magnetic properties. Because of the strong coupling between the
small structural distortions related to the charge-ordering (CO) and the
resistive properties, the presence of the substrate prevents the full
developpement of the charge ordering in Pr$_{0.5}$Ca$_{0.5}$MnO$_{3}$,
especially in the very thin films. For thicker films, the CO state exists, but
is not fully developped. Correlatively, the magnetic field which is necessary
to suppress the CO is decreased drastically from 25 Tesla to about 5 Tesla on
SrTiO$_{3}$ substrates. We have also investigated the influence of the doping
level by studying the case of Pr$_{0.6}$Ca$_{0.4}$MnO$_{3}$.
