A new motility meter for recording the locomotor activity of small laboratory animals is described in detail. The equipment is designed to record simultaneously, but independently, the motility of eight animals (or groups of animals) in separate cages. The functional mechanism is an application of the well known Doppler principle. The use of electromagnetic waves presents the important advantages of contactless detection and freedom from interference of external stimuli with spontaneous activity; both horizontal and vertical components of movement are registered. To test the equipment, motility was studied in rats treated with saline, haloperidol, d,l-amphetamine, and the combination of haloperidol and d,l-amphetamine. Motility, as measured with the Doppler motility meter, proved to be very sensitive to drug-effects.