We present a measurement of the branching ratios Rb and Rc of the Z0 boson to
b and c quarks. We extract Rb and Rc simultaneously using a multi-tag method.
This measurements relies on the unique features of the SLD detector, the
high resolution CCD vertex detector and the micron size beam spot. Since most
of the efficiencies are measured from data the systematic errors are small.
This measurement uses our full data set.