  We present new multicolour CCD photometry of the central part of the globular
cluster M3, mapping the precise position of ~120 RR Lyrae stars (RRab, RRd,
RRc) on the horizontal branch (HB). The location of the double-mode variables
(RRd) is in perfect agreement with recent theoretical results. We find a
significant internal spread of metallicity amongst the RRab variables.
