Traditionally, peptide secretion by endocrine cells and neurons was studied by measuring changes in release in response to experimental perturbations. Now it is possible to directly view dense core vesicles (DCVs), secretory apparatus proteins and individual exocytotic events by imaging fluorescent proteins in living cells. Fundamental insights into peptide release by cultured cells have been made with wide field, confocal and total internal reflection (also called evanescent wave) microscopes. Researchers have also used a variety of fluorescent protein constructs that vary in spectra, pH sensitivity, inducibility, and age dependence. Most recently, these approaches have been applied to transgenic animals so that hormone and neuropeptide release can be studied in vivo.