Mast cells are widely distributed throughout the body, predominantly near blood 
vessels and nerves, and express effector functions in allergic reactions, 
inflammatory diseases, and host defense. The activation of mast cells results in 
secretion of the preformed chemical mediators in their granules by a regulated 
process of exocytosis and leads to synthesis and secretion of lipid mediators 
and cytokines. Their soluble factors contribute to allergic inflammation. Mast 
cells are associated with hypersensitivity reactions, not only in the classical 
immunoglobulin E (IgE)-dependent mechanism but also in an IgE-independent 
manner. In particular, investigations of potential anatomical and functional 
interactions between mast cells and the nervous system have recently attracted 
great interest. To understand these molecular mechanisms in mast cell 
activation, the ability to visualize, track, and quantify molecules and events 
in living mast cells is an essential and powerful tool. Recent dramatic advances 
in imaging technology and labeling techniques have enabled us to carry out these 
tasks with high spatiotemporal resolution using confocal laser scanning 
microscopes, green fluorescent protein and its derivatives, and image analysis 
systems. Here we review our investigations of the dynamic processes of 
intracellular signaling molecules, cellular structure, and interactions with 
neurons in mast cells to provide basic and valuable information for allergy and 
clinical immunology using these new imaging methods.