We, in veterinary medicine, have stained for mast cells "forever".  We find
it interesting that those working with the human species are just now
discovering them.  There are several excellent stains for mast cells,
depending on what tissue architecture one's wishes to see in the background.
        1.  Toluidine Blue - stains mast cells, dark blue with magenta
granules, light blue background. 
        2.  Modified Jenner-Giemsa - stains the same as the T Blue, with
more tissue architecture defined.
        3.  Thionin - stains only mast cells with no background.  The tissue
must be oriented prior to staining.
It should be remembered that mast cells stain differently depending on their
age - either granular or agranular.  Because of thise, stains may look as if
they did not work (as not staining granules), but they are.  Use a canine
mast cell tumor or human umbilicus as a control.  
        If you are interested in the directions to any of these stains,
please contact me directly.

Cheryl
Cheryl Crowder
Chief Technologist
Department of Veterinary Pathology
School of Veterinary Medicine
Louisiana State University
S. Stadium Road
Baton Rouge, LA  70803
(225) 346-3399
FAX (225) 346-3226
ccrowder@mail.vetmed.lsu.edu