The processes of metabolism and excretion which lead to elimination may be described mathematically, and the study of the elimination processes of drugs in general is called pharmacokinetics. The pharmacokinetics of amphetamines are a logical result of drug administration and occur in the body of every species. The maximum plasma concentration of a drug is reached when in-and outflow of a drug in plasma are in equilibrium. Sweat originates from the blood plasma and its composition is mainly determined by the subsequent reabsorption and exchange mechanisms, and the pH of sweat may differ considerably in different individuals. Amphetamines are excreted in saliva and thereby swallowed again. Metabolic degradation and renal excretion both contribute to the elimination of amphetamines. It is known that phenobarbital is able to induce the metabolic capacity of a large variety of drug-metabolizing enzymes. The reactions contributing to the side chain breakdown of the amphetamines generally serve to terminate the activity of the drug.