beta-Hexosaminidase, beta-glucuronidase, arylsulfatase, and tryptase were each released along with histamine from dispersed purified human lung mast cells of 40 to 80% purity by rabbit IgG anti-human IgE. The net per cent release ratio of each enzyme to histamine was determined over all doses of antibody employed to activate the mast cells and over all time points after activation, and indicated the per cent of each enzyme stored in secretory granules along with histamine. By multiplying the net per cent release ratio of each enzyme to histamine by total enzyme content in a preparation of 10(6) mast cells, values for secretory granule content per 10(6) mast cells were found to be 3.8 U for beta-hexosaminidase, 0.03 U for beta-glucuronidase, 0.03 U for arylsulfatase, and 0.9 U for tryptase. Subtype analysis of beta-hexosaminidase by diethylaminoethyl- (DEAE) cellulose chromatography revealed that the B isomer predominates in human mast cell secretory granules, whereas the A isomer predominates in secretory granules of the rat mast cell. Tryptase, the predominant neutral protease of the human mast cell secretory granule, has a m.w. of 130,000 by gel filtration chromatography, whereas the major neutral protease of the rat mast cell is chymotryptic and of 25,000 m.w. The presence of acid hydrolases, a tryptase, and histamine in human mast cell secretory granules suggests that the activated mast cell plays a direct role in the production of acute and subacute inflammation.