With the growing awareness of the neurological effects of many environmental chemicals, there is considerable emphasis being placed on the detection of neurotoxic potential at the screening, or first-tier, level of testing. The authors have developed a neurobehavioral screening battery consisting of a functional observational battery (FOB) and an automated measure of motor activity which can be incorporated into neuropathological studies as well as general toxicity assessments of new and existing chemicals in rats. This approach has been recommended by several expert national and international panels, and has recently been recommended by the US Environmental Protection Agency for testing pesticides and industrial chemicals. The FOB consists of a series of home-cage, open-field, and interactive assessments of the rat's behavior and neurological functions. Motor activity provides an objective apical measure of the rat's neurobehavioral function. In order to assess validity, sensitivity, and specificity, the authors have utilized these test methods to determine dose-response and time-course characteristics of a wide variety of chemicals including pesticides, metals, solvents, and industrial compounds.