The clinical pharmacokinetics of chlorpheniramine are reviewed. Recent studies have established that the half-life of chlorpheniramine is longer than previously reported. Chlorpheniramine has a serum half-life of approximately 20 hours in adults, and elimination from the body is primarily by metabolism to monodesmethyl and didesmethyl compounds. The half-life is increased in the presence of renal dysfunction and decreased in children. The exact mechanism of the presystemic first-pass elimination and the effects of dose levels on the process presently are unclear. Biopharmaceutical and pharmacokinetic studies after single or multiple doses in humans reveal wide interindividual variations in pharmacokinetics. Age, dialysis, urinary pH and flow influence the elimination kinetics of chlorpheniramine. Attention is brought to major issues that need further clarification to optimize drug therapy with this antihistamine. The use of pharmacokinetic parameters of chlorpheniramine for clinical application is discussed.