We consider the field dependence of the microwave resistivity in high-T-c s
uperconductors. We present field-dr-pendent microwave resistivity measureme
nts at 48 GHz on thin YBa2Cu3O7-delta and Bi2Sr2CaCu2O8+delta films. The fi
eld dependence of the microwave resistivity cannot be satisfactorily descri
bed in terms of a single model for the flux motion when both materials are
considered. We introduce and discuss a simple model that incorporates the e
ffect of the enhanced field-induced quasiparticle increase in a superconduc
tor with Lines of nodes in the gap, together with viscous flux motion. A go
od description of the data is obtained, for YBa2Cu3O7-delta as well as for
Bi2Sr2CaCu2O8+x.