We have compared the ability of anti-IgE, calcium ionophore A23187, substance P, compound 48/80, poly-L-lysine, and morphine to release histamine from mast cells of human skin, lung, adenoids, tonsils, and colon. Use of a single collagenase/hyaluronidase dispersion technique for all tissues has allowed comparisons of reactivity to be made that are free from methodological variations. Mast cells from all tissues examined secreted histamine in response to anti-IgE and calcium ionophore A23187. However, only skin mast cells were responsive to substance P, compound 48/80, poly-L-lysine, and morphine. Activation of human skin mast cells by these nonimmunologic stimuli clearly distinguishes them from the mast cells of human lung, adenoids, tonsils, and colon and is indicative of functional heterogeneity within the human mast cells population. We propose that the presence of functional receptor sites for neuropeptides and basic compounds on skin mast cells that are not present in mast cell populations from mucosal or lymphoid sources reflects a specialized role for these cells in vascular homeostasis.