Procedures used to identify or screen for the presence of neurotoxicity are usually designed to test large numbers of animals and are not considered to be as sensitive to subtle effects as more specialized tests for neurobiological dysfunction. For purposes of screening, the use of a functional observational battery (FOB) is now generally accepted. A number of batteries containing different observations and measurements have been developed in several laboratories for rodents, dogs, and non-human primates. FOB used in screening typically assess several neurobiological domains including neuromuscular (i.e., weakness, incoordination, abnormal movements, gait, motor seizures, myoclonia, rigidity and tremor), sensory (i.e., auditory, visual and somatosensory) and autonomic (i.e., pupil response, salivation) functions. Most FOB used for screening do not assess cognitive function (i.e., learning and memory). FOB evaluations can yield important information concerning dose-response characterizatics and data on the onset, duration and persistence of an effect. FOB should be able to differentiate neurotoxicants from non-neurotoxicants and neurotoxicants having different mechanism(s) or site(s) of action.