The plasma ballooning stability of three sets of equilibria characteristic of tokamak, screw pinch, and turbulently heated tokamak has been investigated. Already at low beta, the tokamak becomes ballooning-unstable and enters at higher betas again a stable region when q on axis is larger than unity. The screw pinch remains stable up to high betas and no second stable region can be found. The third equilibrium is always Mercier-unstable in the centre of the plasma.