From 100 rats observed during 1 h, elementary behavioral units were identified, characterized, and behavioral boundaries were established. From this, two main categories were established and named a) basic body postures, and b) posture-associated moving actions. Four subcategories concerning posture-associated moving actions were 1) body-directed actions; 2) actions of interaction with the environment; 3) moving actions without locomotion; and 4) displacement actions with locomotion. This ethological characterization in an open field could be applied to the study of motor effect induced by experimental manipulation of the brain function, at maturity.