Abstract
Radial velocities for a sample of O stars with known distances, from the Catalogue of Galactic O Stars (Cruz-Gonzalez et al., 1974), have served to calculate Oort's constant A. A value around 13 km -1 kpc-1 has been obtained. The solar motion components U0, V0 and the rotation constants a, k were determined assuming the perpendicular components of the solar motion as W0 = 7 km -1 and the distance from the sun to the galactic center, R0 = 10 kpc.
