Abstract Since the original work by [Sir Geoffrey Ingram] Taylor several authors have reported theoretical and experimental calculations on Rayleigh-Taylor and other gravitational instabilities for various fluid and field geometries of magnetohydrodynamical interest. In the particular case of the theta pinch geometry, a Rayleigh-Taylor instability is found to occur in the first (adiabatic) expansion stage of the columns, with experimental growth rates of the proper order of magnitude for this type...