A catalog of Cepheid variables is used to probe the kinematics of the Galactic disk .
Radial velocities are measured for eight distant Cepheids toward \ell = 300 ^ { \circ } ; these new Cepheids provide a particularly good constraint on the distance to the Galactic center , R _ { 0 } .
We model the disk with both an axisymmetric rotation curve and one with a weak elliptical component , and find evidence for an ellipticity of 0.043 \pm 0.016 near the Sun .
Using these models , we derive R _ { 0 } = 7.66 \pm 0.32 kpc and v _ { \it circ } = 237 \pm 12 km s ^ { -1 } .
The distance to the Galactic center agrees well with recent determinations from the distribution of RR Lyrae variables , and disfavors most models with large ellipticities at the solar orbit .