Kryptonite is a glowing green mineral that emits a potent radiation that weakens Kryptonians in its vicinity. Batman keeps it in an "overwhelmingly impenetrable" vault in the Batcave. Robin used it to incapacitate the mind-controlled Superman at the Watchtower. It appeared to affect Superboy, who was restraining Superman, to a lesser extent.
- 126. "Auld Acquaintance"