1 Introduction.- 2 Ultrastructure of Human Mast Cells.- 3 Ultrastructure of Human Basophils.- 4 In Vitro Studies of Human Mast Cells.- 4.1 Human Mast Cell Granules and Lipid Bodies.- 4.1.1 Differences in Structure.- 4.1.2 Differences in Content.- 4.1.3 Differences in Mechanism of Formation...- 4.1.4 Differences in Behavior During Degranulation.- 4.1.5 Differences in Behavior During Recovery from Degranulation.- 4.2 Anaphylactic Degranulation of Human Lung Mast Cells In Vitro.- 4.3 Recovery from Anaphylactic Degranulation of Human Lung Mast Cells In Vitro.- 4.3.1 Early Recovery Events.- 4.3.2 Late Recovery Events.- 4.3.3 Mixed Recovery Patterns.- 5 In Vivo Studies of Human Mast Cells.- 5.1 Anaphylactic Degranulation of Human Mast Cells In Vivo.- 5.2 Piecemeal Degranulation of Human Mast Cells In Vivo.- 5.3 Activated Human Mast Cells Have Increased Lipid Bodies.- 5.4 Mast Cell Shedding.- 6 Mast Cell Morphologic Cycles.- 6.1 In Vitro.- 6.2 In Vivo.- 7 Concluding Remarks.- 8 Summary.- References.