AbstractStaining for mast cells in undecalcified sections of bone was evaluated with a variety of toluidine blue (TB) preparations. Attention was given to color change in granules, nuclear clarity, background staining, and appearance of bone. Our buffered TB stain, which was developed to highlight bone detail, resulted in violaceous staining of the granules in mast cells, often restricting their identification. An acidified TB stain and a new stain of TB dissolved in 30% ethanol resulted in purple granules. Prestaining with Congo red prior to acidified TB allowed good bone detail and full expression of metachromasia with red appearance of the granules, giving the best view of the mast cell. (The J Histotechnol13: 49, 1990)