Metoprolol is a lipophilic beta(1) selective adrenergic receptor antagonist used in antihypertensive therapy. It is metabolized by the protein product of the cytochrome P450 2D6 (CYP2D6) gene. Few studies have been performed on the association between the beta(1) adrenoreceptor, CYP2D6 polymorphism and blood pressure. The one reported here is a prospective, observational, clinical study in Chinese Han hypertensive patients on the combined influences of CYP2D6 and beta(1) adrenoreceptor polymorphisms on the therapeutic effects of metoprolol in 300 out-patients with essential hypertension. The same dose of metoprolol achieved different therapeutic effects in patients with different CYP2D6 and beta(1) adrenoreceptor polymorphisms. Additionally, different doses of metoprolol could achieve the same therapeutic effects in patients with different CYP2D6 and beta(1) adrenoreceptor polymorphisms. Knowledge of the combination of CYP2D6 and beta(1) adrenoreceptor polymorphisms may be used to guide antihypertensive therapy using beta(1) adrenoreceptor antagonists.