Abstract
A method is described for the enzymic dispersion into their component cells of cardiac tissues from the rat and guinea-pig. The resulting suspensions containca. 1% free mast cells and exhibit a low spontaneous release of histamine. The reactivity of these cells towards a number of defined chemical histamine liberators is compared with that of other connective tissue mast cells from the same animals. The results obtained are discussed in terms of the general functional heterogeneity of mast cells from different locations.