Recent progress in insect metamorphosis is reviewed, emphasizing two aspects - endocrine systems and epidermal-cuticular systems. In the first part, the neuroendocrine system of the brain is discussed. For two classes of hormones - prothoracicotropic hormone (PTTH) and eclosion hormone (EH) - the structures have recently been elucidated and their neurosecretory cells localized. In addition, work on the biosynthesis, secretion, metabolism, and mode of action of the molting hormone, ecdysteroid, is summarized. In the second part, the molecular transformation in the epidermal-cuticular system during metamorphosis is detailed, e.g. the molecular mechanisms of hardening and pigmentation of cuticles after ecdysis. This part also comprises articles on the control of expression of stage-specific genes in epidermis development.