Spells (3e)

The warded creature gains partial protection from undead creatures who use negative energy and certain weapons and spells that drain energy levels. The negative energy protection spell uses positive energy, which can offset the effects of a negative energy attack. Each time the warded creature is struck by a negative energy attack that drains levels or ability scores, it rolls 1d20 + caster level against a DC of 11 + the attacker’s HD.

If the warded creature succeeds, the energies cancel with a bright flash of light and a thunderclap. The warded creature takes only hit point damage from the attack and does not suffer any drain of experience levels or ability scores, regardless of the number of levels or ability score points the attack would have drained. An attacking undead creature takes 2d6 points of damage from the positive energy. An attacking caster or weapon receives no damage.

If the warded creature does not succeed, the negative energy attack deals its normal damage. An attacking undead creature in such a situation does not take any positive energy damage.