H1 antihistamines have similar efficacy in the treatment of allergic disorders; however, they differ in terms of their chemical structure, clinical pharmacology, and safety. This review focuses on the clinical pharmacology (pharmacokinetics and pharmacodynamics) of the newer oral H1 antihistamines (acrivastine, cetirizine, desloratadine, ebastine, fexofenadine, levocetirizine, loratadine, and mizolastine). Understanding the pharmacokinetics and pharmacodynamics of these H1 antihistamines provides an objective basis for selection of appropriate dosages and dose intervals. Pharmacokinetic and pharmacodynamic studies provide a rationale for the modified dosage regimens that may be required in special populations, such as the very young, the elderly, those with hepatic or renal dysfunction, or those taking other medications concurrently. Many H1 antihistamines are currently available for use. Clinical pharmacology studies help physicians to select the best H1 antihistamines for their patients.