A technique of Positron Emission Particle Tracking (PEPT) was used to obtain information on the flow behavior of coarse particles suspended in pseudoplastic liquids agitated by axial-hydrofoil Lightnin impellers A320 and A410. PEPT enables the position of a 600 μm radioactive particle tracer inserted inside one of the suspended particles to be detected many times per second and its full trajectory followed inside the vessel. Particle trajectory analysis yielded information on particle circulation, velocity distribution, and spatial occupancy. The minimum speed for complete particle suspension, Njs, was also determined. The well-known Zwietering correlation failed to predict the measurements by a substantial margin, suggesting that it is inadequate for viscous non-Newtonian liquids.