Using a 5-GHz parallel-plate resonator, several Gd 123 films and one Tl 2212 film have been studied as a function of microwave power. The variation of the surface resistance as a function of dc magnetic fields applied parallel to the crystallographicc axis reflects the gross microstructure of the films. Two broad categories of behavior are observed in dc field. The evidence for intrinsically limited power dependence is discussed in terms of impedance plane analysis.