The need for rapid and inexpensive tests in toxicology has prompted several advisory panels to recommend motor activity as a screen for neurotoxicity. Since motor activity reflects the general status of the organism, disruption produced by a variety of neurotoxic and non-neurotoxic mechanisms should be manifest as changes in motor activity. Studies of motor activity are useful, therefore, when no a priori reason exists for predicting a particular behavioral effect of exposure to a chemical. Activity measurements are also useful in characterizing the toxic properties of a chemical.