The influence of side leakage on the onset of Taylor vortices in high-speed journal bearings is studied by observing the effects of varying the eccentricity of, and the axial flow through, an annulus. The apparatus permits of both sharp and smooth entries to the annulus. Flow visualization is achieved by means of aluminium paint pigment suspended in the test fluid. It is shown that both the eccentricity and the axial flow have a marked effect on the critical Taylor number. Evidence is presented for the co-existence of two systems of vortices within the annulus.