Optical microscopy has been used to study the flow behaviour of a dispersion of plate-like particles. The sample of hexagonal discs of nickel hydroxide stabilised with a short-chain, charged polymer was investigated over a range of shear rates up to 100 s(-1) with a polarising, transmitted light microscope. Direct evidence for a shear-induced phase transition with a change in alignment of the particles is seen. At low shear rates (below 1 s(-1)), the discs aligned with normals in the flow direction while at high shear rates (above 18 s(-1)) the discs were aligned with their normals in the gradient direction. Between these two shear rates a striped texture consisting of both the low and the high shear rate structures was observed. These results are compared with previous studies using theological measurements, scattering and diffraction.