The deposition kinetics of polymeric microspheres (average diameter 8.742 mu m, density 1.50 g.cm(-3)) on smooth silica plates was determined experimentally. The measurements were carried out in a sedimentation cell using a direct microscope observation technique supplemented by the image analysis. The experimental data were interpreted in terms of the ballistic deposition (BD) model, where the irreversibility of the adsorption is assumed. It was found that both deposition kinetics and the jamming coverage (determined to be 0.60 +/-0.02) were in quantitative agreement with the ED model. Our experimental data constitute, therefore, a direct proof of the validity of this model for characterizing particle deposition processes driven by a strong gravitational force field.