The translational and rotational velocities of a sphere rolling down an inclined plane at low Reynolds number were measured as a function of the angle of inclination of the plane. Both 140 &mgr;m glass and 6350 &mgr;m diam acrylic particles were used. A theoretical model including the effects of particle surface roughness was developed, and is in quantitative agreement with the measurements. In addition, statistically significant velocity fluctuations were measured and are explained by variation in the coefficient of friction of the sphere. The disagreement between the measurements of Carty (B.S. thesis, Massachusetts Institute of Technology, 1957) and the theory of Goldmanetal. [Chem. Eng. Sci.22, 637 (1967)] is explained.