It was shown theoretically in a previous paper that during the laminar flow of a suspension through a tube, and for least action, a suspended particle would follow a path adjacent to the tube axis. In general, therefore, a particle entering a tube non-axially would be expected to move with a component of translation normal to the streamlines and directed towards the axis. In the present paper this theory is developed and leads to the conclusion that for a particle at any given point in the tube this component increases with particle size. Experiments are described in which streams of coloured particles of mixed sizes suspended in water were admitted at a given point on the horizontal diameter of a tube placed horizontally, through which a steady flow of water was maintained. These coloured streams diverged on entry to the water and formed filaments in a horizontal plane. A study of the lateral movement of these filaments relative to one another, as the point of their admission to the tube and the rate of flow of water in the tube are varied, leads to the conclusion that lateral forces act on the suspended particles. Such forces, the magnitudes of which increase with particle size and with mean shear gradient, result from the motion of the particles in non-uniform velocity gradients. The motions observed lead directly to a simple flow mechanism, independent of particle configuration and orientation, which is shown to be qualitatively consistent with a number of well-established phenomena.