We have re-estimated the surface density of the Galactic disk in the solar neighborhood within ± 0.4 kpc of the Sun using parallaxes and proper motions of a kinematically and spatially unbiased sample of 1476 old bright red giant stars from the Hipparcos catalog with measured radial velocities from Barbier-Brossat & Figon (2000). We determine the vertical distribution of the red giants as well as the vertical velocity dispersion of the sample, (14.4 ± 0.3 km/sec), and combine these to derive the surface density of gravitating matter in the Galactic disk as a function of the Galactic coordinate z. The surface density of the disk increases from 10.5 ± 0.5 M ⊙ / pc 2 within ± 50 pc to 42 ± 6 M ⊙ / pc 2 within ± 350 pc. The estimated volume density of the Galactic disk within ± 50 pc is about 0.1 M ⊙ / pc 3 which is close to the volume density estimates of the observed baryonic matter in the solar neighborhood.

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