Particle Tracking Velocimetry (PTV), in conjunction with the refractive index matching technique and laser induced fluorescent (LIF) tracer particles, was used to overcome the visualization problem in a particle suspension. A square test section was filled with the particle suspension and impulsively heated from the bottom wall while the two facing vertical walls were kept at a constant temperature. The two-dimensional velocity fields, particle distributions in a plane and the wall temperature fields were visualized simultaneously using three cameras. The results showed peculiar flow patterns such as the formation and vanishing of two-layer convection cells which were distinct from those in a clear, particle-free fluid. Sedimentation driven convection is thought to be the fundamental mechanism for the formation of these two layer convection cells. The overlying particle-free-layer convection was started by the release of the heated clear fluid at the interface between the particle-free layer and the suspension. (c) 2005 Elsevier Ltd. All rights reserved.