With the help of a trial function, the energy principle is used to study the stability of an axisymmetric, arbitrary-cross-section, arbitrary-aspect-ratio toroidal plasma to a particular class of axisymmetric modes which are antisymmetric with respect to the equatorial plane. It is shown that configurations with toroidal current decreasing monotonically towards the boundary, which are maintained by an external magnetic field with negative decay index, must always be unstable in the absence of any external stabilizing agencies such as active or passive feedback.