Radiative corrections and instability of large Q-Balls

We discuss stability of Q-balls interacting with fermions in theory with small coupling constant g. We argue that for configurations with large global U(1)-charge Q the problem of classical stability becomes more subtle. For example, in model with flat direction there is maximal value of charge for stable solutions with Q~1/g^4. We study origin of additional instability and discuss possible ways to avoid it.