Tiagra STI shifters to ultegra RD?

Question

Can someone tell me if it's possible to run a set of Shimano Tiagra STI shifters to an Ultegra rear derailleur?

Am i right in assuming the only thing that would prevent this is if i mix 9 and 10 speed components (no desire really in doing this...just wondering about the tiagra to ult)

Thanks

Answer 1

as long as they are both 9sp it will work.

Answer 2

Yep, as long as the speed matches you are good to go. They are interchangable with 105 and DA as well.