Three sets of experiments were carried out in a Y water maze in which mice had to swim toward the light or the dark, in two different procedures. The first procedure involved orientation toward a light source (L procedure), corresponding to natural preference, the latter involved orientation toward the dark (D procedure), corresponding to the acquisition of a new pattern of behavior. In pretrial drug treatments caffeine was administered to two groups of naive mice, tested under one of two experimental conditions. Posttrial drug treatments were made in animals learning the D procedure. Pretrained mice in the L or D procedure were finally injected with increasing doses of the drug. The results show that caffeine administration to naive animals was followed, in the D procedure, by a facilitation of learning and consolidation processes, and in the L procedure by improvements of the natural tendencies. Behavioral disruption followed treatment with the drug in mice pretrained in the D procedure, while only very high doses caused disruption in mice pretrained in the L procedure.