I broke my Ignition Key in the lock..
 

Uh its my neighbor's car..and not a Mercedes, but the post "counts" since I was working on my Mercedes when I was approached by my neighbor, who is on a tight budget and depends on this car for transportation and she won't let me return to reinstalling my transmission until I get this done..the lady broke her key in the ignition lock. However if I place the remaining portion of he Key in the lock, I can start the car, etc.

The car is a 1988 Corolla..

Is there a procedure or hope of extracting the broken part of the Key?

I broke my Ignition Key in the lock..

Hey, I had one of those. Came with my wife as an 'accessory'. Gave it to my little brother, and it is still in service with 230k miles.
I've even taken the entire dash (including ignition) apart twice. Once because it was stolen, and again when the wiring harnesses melted down.

Anyways, short of a time-consuming disassembly, I would try tweezers or a hemostat. Possibly a dental pick, or 2 picks working together.

Someone once claimed they were able to pull this trick off with a drop of super glue, though if you used too much, it could make matter worse.

Unfortunately, the cylinder design is not such that you can poke something through from the back side to push the key out, which worked for me once on another car.

How far in is the break?

Might be time to install a push button starter switch... LOL!

how 'bout
 

I just stuck a magnet to my key, could you work that in somehow? do you remember as a kid making an electric magnet in shop? you wind wire around a nail and hook it up to a 9v battery or some thing? then you could stick this tiny high powered magnet in there and hopefully get the bugger out.

cdt

Go to the auto parts store and get a set of picks -- there are four in the package, straight, 90 degree, hooked, and a funny twisted on.

The funny twisted one will probably hook under the cut side of the key, allowing you to pull it out.

Peter

Use a Broken Key Extractor.

Although they are inxepensive, you may be able to borrow one from a local locksmith, or since you can start the car, drive it to a locksmith.

-Bryan