Harm charges a subject with negative energy that deals 10 points of damage per caster level (to a maximum of 150 points at 15th level). If the creature successfully saves, harm deals half this amount. Harm cannot reduce the target's hit points to less than 1.

If used on an undead creature, harm acts like heal, wiping away the injuries and afflictions of an undead subject.  It immediately ends any and all of the following adverse conditions affecting the target: ability damage, blinded, confused, dazed, dazzled, deafened, diseased, exhausted, fatigued, feebleminded, insanity, nauseated, poisoned, sickened, and stunned. It also returns 10 hit points of damage (per level of the caster) to the subject, to a maximum of 150 points at 15th level.

Harm used on an undead subject does not remove negative levels or restore permanently drained ability score points.