Mariner 10 images of Venus taken at several phase angles were photometrically reduced. The analysis shows that the phase function of the cloud particles is not isotropic, as had been deduced earlier from the brightness distribution on spacecraft images taken at a single phase angle, but has a broad minimum near 60¿ and is forward-scattering. The scattering properties are in quantitative agreement with previous deductions from earth-based polarization measurements by Hansen and his associates.