Bulge and halo material is often invoked to explain the absence of bars in the majority of disc galaxies, although the amount required is not known, in general, and is sensitive to the shape of the rotation curve. Here we show that the necessary fraction of spherical material is also affected by the degree of random motion amongst the disc stars. Quite moderate velocity dispersion has a strong stabilising influence and our hottest disc is stable without any halo (see also Kalnajs, this volume).