stop poisons or diseases or any of that. It doesn't stop magical attacks, either. It works for melee/hand-to-hand combat. It seems to cut down on damage from ranged attacks a bit, but I'm not 100% positive about that part. I put a ring on my toon that reduces damage from missile attacks, and she never seems to take any damage from those. Try jewelry enchants for every thing other than physical damage. It helps.