Abstract: Carnoys fluid and neutral buffered formalin(NBF)have been proved to be good fixatives for preservation of mast cells in pig,cattle and sheep except NBF blocked staining of most porcine mast cells,especially those located in intestinal mucosa (MMC) and in thymus medulla(TMMC).Both toluidine blue and Alcian blue were the excellent stains generally,but Alcian blue stained more porcine mast cells than did toluidine blue (P<0.01).Staining with toluidine blue of a wide pH range(from 0.1 to 7.0)showed that porcine mast cells were not very pH dependent,but the dye at pH 0.5 seemed to have the strongest affinity for all mast cells in pigs and it was also suitable for bovine and ovine mast cell staining.In the three species,unlike in rodents,the Alcian blue method did not distinguish between mast cells in the intestinal mucosa (MMC) and those in the connective tissue of the intestinal submucosa,tongue and skin (CTMC).Porcine CTMC,but not MMC,fluoresced strongly when stained with berberine sulphate or with a mixture of berberine sulphate and acridine orange.It suggested that porcine CTMC contained heparin proteoglycan.