Multicellular organisms develop through a series of coordinated steps leading cells to differentiate, migrate, and arrange themselves into specific organs with specialised functions. The importance of micronutrients like zinc and copper in these interdependent events has long been recognised. Zinc deprivation arrests cell division and induces congenital malformations of foetal organs. Many studies document the essential role of copper in mammalian growth and development. On the other hand, large quantities of free metal ions can be toxic to biological systems. The mechanism by which organisms accumulate, sense and respond to metallic ions is a critical aspect of cellular growth control. Metallothioneins, a family of closely related metal-binding proteins, are considered to be key molecules involved in some major biological processes in relation to the metabolism of essential and toxic metal ions. Information on the occurrence, metabolic roles and homeostasis of zinc and copper in oocytes and embryos of non-mammalian vertebrates are very limited. In this article we review recent findings on the correlation between heavy metals and metallothioneins during embryogenesis in oviparous vertebrates, and on the molecular events involving zinc, copper and metallothioneins in these organisms.