Trolls and other particularly hardy creatures can regenerate damage at an incredible rate.
A model with the Regeneration special rule is permitted a special regenerate saving throw after it has failed any armour save it may have, instead of taking a ward save (if it has one). If a model has both aand Regeneration, you must choose which save is used.
To take a regeneration save, roll a D6. On a 1-3, the wound affects the model normally, even its incredible constitution has not prevented this injury. On a 4-6, the damaged flesh regrows, leaving not even so much as a scar to indicate the injury was ever there – the wound is discounted, exactly as if it had been saved by other means.
Whilst the type of regeneration described above is the most common form, some creatures do have a lesser or greater chance to regenerate. Where this is the case, the score required to regenerate will be shown in brackets after the special rule, e.g. Regeneration (5+) would indicate that the model had the Regeneration rule, but that it only worked on a 5+, whilst Regeneration (2+) would mean that the creature would pass its regeneration save on a 2 or more!
Wounds caused bycannot be regenerated, and if a unit is wounded by a Flaming Attack it loses the Regeneration rule for the remainder of the phase (it can be used later in the turn, though – it just takes a short time for the Regeneration to overcome the flames).