Vanadium pentoxide gels and sols, V2O5,nH2O, exhibit a ribbon-like structure. They form colloidal suspensions (also called Zocher phases or ‘tactophases’) which are clearly shown here to present a homogeneous lyotropic nematic phase for concentrations larger than ≈0·12mol 1−1. Classical threaded textures were observed in polarized light and small angle X-ray scattering patterns of oriented samples displayed a diffuse spot quite comparable to that of the Tobacco Mosaic Virus. For a sample of volume fraction φ ≈ 5 per cent, the V2O5ribbons are separated by about 160 Å, so that the cross sectional area of the ribbons is about 1300 Å2, in agreement with previous estimations by electron microscopy.