Since you need only touch your enemy, you make a touch attack instead of a regular attack. Touching an opponent with a touch spell is considered to be an armed attack and therefore does not provoke attacks of opportunity when it is discharged on an armed opponent. The touch spell provides you with a creditable threat that the defender is obliged to take it into account just as if it were a weapon. However, the act of casting a spell does prove an attack of opportunity, so you may want to cast the spell and then move to the target instead of vice versa. Touch attacks come in two types: melee touch attacks (for touches made with, say, your hand) and ranged touch attacks (for touches made with magic rays, for example). You can score critical hits with either type of attack. Your opponent's AC against a touch attack does not include any armor bonus, shield bonus, or natural armor bonus. His size modifier, Dexterity modifier, and deflection bonus (if any) all apply normally.