Abstract. Experiments on Spherical Tori (ST) show that plasma MHD activity may strongly deteriorate the confinement of energetic ions. Therefore, a study of the interplay of MHD modes and energetic ions is of large practical importance. Such a study is carried out in this work, where both the influence of the energetic ions on plasma MHD activity and the MHD-induced transport of energetic ions are considered. In particular, it is shown that in STs, in contrast to conventinal tokamaks, the presence of trapped energetic ions may have a destabilizing influence on the ideal kink instability and the collisionless tearing instability. On the other hand, it is found the transport of energetic ions caused by reconnection events (sawtooth oscillations, internal reconnection events and non-ideal fishbones) has a number of peculiarities in STs. Specific calculations of the change of the neutron flux caused by the particle redistribution by reconnection events and of the loss fraction of the energetic ions are carried out for the Neutral Beam Injected (NBI) ions in the National Spherical Torus Experiment (NSTX). Results of the calculations are compared with experimental observations.