"

 Postdoctoral researchers 

Sheldon and Leonard do not appear to be postdoctoral fellows, as they do not seem to be awaiting another position nor is their research supervised. Dr. Eric Gablehauser is their boss, not an advisor. As postdocs, they may have been able to teach the research seminar once, so this is not conclusive. Particularly, Sheldon is a double Ph.D. holder and child prodigy who was a visiting professor at 15, so he would not be in such an appointment. For the most part, they do not appear as postdocs. There is ambiguity to their positions, but they have only been shown having research responsibilities, so they may be research professors (besides Sheldon wouldn't waste his time teaching ""labberdoodles""). 68.227.32.148  "