MDhillslug... you definitely can use mtn bike rear derailleurs on a road bike. It sounds as though many of the above people have done exactly that, and I have set up MANY customers like that myself. The concern is that if you have a Shimano drivetrain, then obviously make sure that you use Shimano rear derailleurs. Whether you are using bar end shifters, or STI shifters.. it definitely WILL work. You can not mix Shimano and SRAM shifters and mtn derailleurs though.