The proper evaluation of adrenergic drugs is important not only in understanding the theoretical aspects of adrenoceptors, but also in the utilization of these substances in therapeutics. Currently, chemicals are being synthesized for organ receptor specificity. Since absolute specificity is practically impossible, investigators look for relative selectivity. Occasionally, judgment regarding organ specificity may be based on few- fold differences between the activity of a drug in different tissues. To arrive at such a conclusion, a critical evaluation of drugs is important. Hence, evaluation from the point of view of quantitation and the factors which affect quanitation is emphasized.