Histoneters;
Re: the many methods for detecting mast cells.
No one mentioned the Chloroacetate Esterase technique, which, for my money, its the most specific, reliable and easiest method out there.
Basically, Mast Cells are very rich in esterase. This is one of the few enzymes that withstands paraffin processing, and is therefore very easy to detect it in these cells.  The only other cells that are rich in this enzyme are cells of the  granulocytic series, but, these are easy to tell from mast cells, by their morphology.  Sigma has an inexpensive and easy to use Naphthol AS-D Chloroacetate Esterase kit (91-C) which makes the detection of this enzyme a breeze.
Try it, you'll like it.

Method
1. Bring paraffin section to water in the usual maner.
2.Incubate sections in Chloroacetate solution for 15 min at 37C.
                                    (prepare chloroacetate as per kit instructions)
3.Rinse in water.
4.Counterstain for 1 min in Gills heamatoxylin. (supplied in kit)
5.Rinse in water.
6.Blue sections briefly in lithium carbonate solution.
7.Mount in an aqueous mounting media.

Results
Mast Cells -- brilliant red
Granulocytes -- red
Nuclie-- blue

Kerry Beebe ART
Kelowna Gen Hospital
Kelowna B.C. Canada
bbracing@silk.net