An experimental study of the migration of dilute suspensions of particles in Poiseuille flow at Reynolds numbers Re = 67–1700 was performed, with a few experiments performed at Re up to 2400. The particles used in the majority of the experiments were neutrally buoyant spheres with diameters yielding a ratio of pipe to particle diameter in the range D/d = 8-42 . The volume fraction of solids was less than 1% in all cases studied. The results of G. Segré & A. Silberberg have been extended to show that the tubular pinch effect in which particles accumulate on a narrow annulus is moved toward the wall as increases. A careful comparison with asymptotic theory for Poiseuille flow in a channel was performed. Another inner annulus closer to the centre, and not predicted by this asymptotic theory, was observed at elevated Re. As is increased, the distribution of particles over the cross-section of the tube at the measurement location, lying at a distance L = 310D from the entrance, changes from one centred at the annulus predicted by the theory to one with the particles primarily on the inner annulus. The case of slightly non-neutrally buoyant particles was also investigated. A particle trajectory simulation based on asymptotic theory was performed to facilitate the comparison of theory and the experimental observations.