The author contended opposite pharmacological effects resulting from lithium and amphetamine. Three groups, each one consisting of four rats, were put on chronic lithium condition to measure its effects on amphetamine hyperactivity. This condition was effected after appropriate handling and saline control periods and the baselines for drug activity were measured. In young rats (150-200g), lithium significantly decreased d-amphetamine hyperactivity (and probably other effects, like anorexia) while producing little effect on amphetamine stereotyped behavior (ASB). If confirmed, this fact may prove of marked importance in further localizing and studying the pharmacology of lithium. However, this observation was true in only three rats of the first group. All other rats, of the older group or of the other strain, showed only ASB, a fact that also deserves further study because it seems to contradict previous important reports.