Measurement of $Z \to \mu \mu$ and $W \to \mu \nu$ rates in CMS

We discuss the possibility of performing precise measurements of the rates of pp->Z->mu^+ mu^- and pp->W->mu nu processes in CMS. The systematic uncertainties in a conservative scenario, assuming a non-optimal detector and leading-order estimates, are found to be 2.3% for Z->mu mu and 3.3% for W->mu nu. These uncertainties will be largely reduced with the use of improved calibrations and next-to-leading-order (NLO) programs. Some preliminary studies on parton-density-function sets and NLO Monte Carlos are also presented. A measurement of the luminosity from these rates with a 6-7% accuracy seems also feasible.