Calculations of Q including the effects of velocity diffusion, finite ion temperature, electric fields and charge exchange are presented. It is found that if all charge-exchange fast ions are lost then Q is severely reduced for a neutral fraction, nn/ne⪆7 × 10−6. These losses are reduced by re-ionization of the charge-exchanged fast ions. Calculations for the case of a two-component tokamak show that the effective charge-exchange rate is typically reduced by 2.5−4 times owing to re-ionization. With allowance for this, it is found that, in a stationary system, the plasma loss rate nτp must be greater than 1012 cm−3 to achieve a Q greater than unity.