A single 200‐μm particle is injected into a 0.25% w/w solution of a commercial polyisobutylene (M v =1.5×10 6 ) in a polybutene solvent, held between a plate and a 21‐cm disc. When rotation of the disc at 5.7 rpm is begun with a disc‐plate separation of 5.4 mm, the particle initially located at a distance r5.1 cm migrates away from the axis with about the same speed. This sharp reversal in the direction of migration with such a small change in the initial location is not expected on the basis of any current theory. Increasing the rate of rotation or decreasing the disc‐plate separation increases this critical r for reversal, while doubling the particle radius had no significant effect.