The present status of pharmacokinetics is reviewed. Pharmacokinetic models and the basic concepts involved in applying models to blood, urine, bile, and tissue levels of drugs and metabolites are discussed. An outline of methods for pharmacokinetic analyses is proposed. Special emphasis is given to the determination of bioavailability of a drug from various dosage forms. Uses of pharmaco-kinetics in determining sites of drug action and in determining a clinical metabolic profile are suggested. The perturbations of magnitudes of pharmacokinetic parameters among individuals challenged with the drug can be used as a diagnostic tool in evaluating the state of dynamic processes, the presence of metabolic diseases and genetic abnormalities, and the failure of physiological functions. The use of pharmacokinetics and the prediction of chronic dosing regimens are reviewed. Typical curves depicting predicted blood levels on repetitive dosing are presented.