  We report new spectroscopic observations of the recently discovered
transiting planet OGLE-TR-56b with the Keck/HIRES instrument. Our radial
velocity measurements with errors of ~100 m/s show clear variations that are in
excellent agreement with the phasing (period and epoch) derived from the OGLE
transit photometry, confirming the planetary nature of the companion. The new
data combined with measurements from the previous season allow an improved
determination of the mass of the planet, M_p = 1.45 +/- 0.23 M_Jup. All
available OGLE photometry, including new measurements made this season, have
also been analyzed to derive an improved value for the planetary radius of R_p
= 1.23 +/- 0.16 R_Jup. We discuss the implications of these results for the
theory of extrasolar planets.
