Spell Opportunity

 
Prerequisite(s): Character Level 21+, Spellcraft 25+ ranks, Combat Casting, Combat Reflexes, Quicken Spell
 
Benefit: Whenever the character is allowed an attack of opportunity, he or she may cast (and attack with) a touch spell as the character’s attack of opportunity. This incurs attacks of opportunity just as if the character had cast the spell normally.
 
Source: Epic Level Handbook