  We present measurements of the microwave surface resistance Rs and the
penetration depth lambda of YBCO:123 crystals. At low T obeys lambda(T) a
polynomial behavior, while Rs displays a characteristic non-monotonic
T-dependence.
  A detailed comparison of the experimental data is made to a model of d-wave
superconductivity which includes both elastic and inelastic scattering. While
the model reproduces the general features of the experimental data, three
aspects of the parameters needed are worth noting. The elastic scattering rate
required to fit the data is much smaller than measured from the normal state,
the scattering phase shifts have to be close to pi/2 and a strong coupling
value of the gap parameter 2\Delta(0)/kTc = 6 is needed. On the experimental
side the uncertainties regarding the material parameters lambda(0) and
Rs,res(0) further complicate a quantitative comparison.
  For one sample does Rs,res(0) agree with the intrinsic value which results
from the d-wave model.
