Dear Mary,

Endosomes come in many varieties -Early, late, recycling etc etc. If you need markers then I would use Rab5 and EEA1 proteins for early endosomes. LAMP1, LAMP2 and Rab7 for late endosomes/lysosomes, Rab11 for multivesicluar bodies, Rab4 for recycling endosomes. There are excellent antibodies available for all of these proteins. Ina addition, the permeabilisation method used is very important. I use a 20min 2%PFA/PBS fixation and then a Saponin based protocol for permeabisation and staining. This helps preserve vesicle shape/size and integrity. 

Let me know if you need more details or protocols.

good luck!

 Hi Mary,

molecular probes of Life technologies offers easy products to localize endosome or lysosomes for fluorecent microscopy