An overview is given of endpoint measures used or to be used in studying developmental neurotoxicity in environmentally exposed children. A variety of neurodevelopmental assessment methods is available covering either more general or rather sepcific aspects of the neuromotor or the neurobehavioral development, respectively. The available assays, not covered in any exhaustive manner, are classified into (1) neurodevelopmental assays for neonates, (2) neurodevelopmental assays for infants and older children, and (3) assays for cognitive development. Illustrative examples are given to demonstrate the use of several such assays in prospective cohort studies on neurodevelopmental effects of inorganic lead and of polychlorinated biphenyls (PCBs). Using these case studied crucial problems of the causative interpretation of findings due to interactions and confounding are discussed.