If you do a quick DAPI (or Hoechst or whatever DNA stain you use) you
should be able to pick up dots in the cytoplasm - it isn't a definitive
Mycoplasma stain, but it will tell you if there are critters hanging out
in your cells. 

You can buy test kits from various companies, but for quick and dirty, I'd
go DAPI.

Hope the tests are negative!

Tamara Howard
CSHL