A small amount of polymer particles with diameters in the 100 μm range can be used as an ensemble of “microdivers” to study sedimentation velocities of polydisperse submicron particles in concentrated opaque suspensions. This tracer technique, based on Berg's (1941) diver method, is simple, measures velocities directly, and does not require underlying theory beyond conservation of momentum. It confirms that the polymer tracers reside at the position in the suspension where the suspension density corresponds to their own density. Aqueous inorganic suspensions of 250–750 nm α-alumina particles were studied, which is electrostatically stabilized with nitric acid in water, using ∼100 μm polymethylmetacrylate and polystyrene particles as tracers. Experiments were compared with predictions by state-of-the-art continuum models for multicomponent sedimentation to underpin the validity of the tracer technique.