Manganese, zinc and copper are essential for normal prenatal and neonatal development. Manganese deficiency causes skeletal abnormalities, congenital ataxia due to abnormal inner ear development, and abnormal brain function. Depression of mucopolysaccharide synthesis and manganese superoxide dismutase activity may be fundamental to ultrastructural and other defects. In copper deficiency, neurological and skeletal abnormalities are due to impairment of phospholipid synthesis and collagen crosslinking, and possibly to low activity of copper metalloenzymes. The fundamental defect leading to the extremely teratogenic effects of zinc deficiency is related to depressed synthesis of DNA. In the neonatal period, poor survival and growth and depressed function of the immune system are salient features. Developmental patterns of trace element concentrations in various tissues suggest that important changes in metabolic regulation of trace elements may occur during the neonatal period. This hypothesis is being investigated by studies of molecular localization of trace elements in certain neonatal tissues, in conjunction with similar observations in milk.