This article reviews the basic principles of pharmacodynamics and pharmacokinetics, with a special emphasis on the pharmacologic considerations that must be taken into account when treating the patient with respiratory disease who is also pregnant or nursing the neonate. A description of the four classes of therapeutic agents used for COPD is given with a discussion of the scientific evidence for their safety during pregnancy. The understanding of asthma suggests that bronchodilators relieve the symptoms, while antiinflammatories suppress the disease. Direct administration to the target tissue by inhalation of the bronchodilators (beta-adrenoreceptor agonists and anticholinergics) and immunosuppressors (corticosteroids and cromolyn) leads to low systemic levels of these drugs, which reduces fetal drug exposure. Oral administration of beta-adrenoreceptor agonists, corticosteroids, and theophylline may be necessary to obtain sufficient maternal lung function and ensure adequate oxygenation of the fetus. This must be carefully weighed against the potential fetal and maternal risks involved with increased systemic levels of these drugs. A brief description of classes of drugs used for upper respiratory diseases (antihistamines, alpha-adrenergic agonists, corticosteroids, antitussives, and expectorants) and their safety during pregnancy is also given. There is concern that most alpha-adrenergic agonists increase blood pressure at therapeutic doses needed to relieve nasal congestion. Therefore, for pregnant patients requiring decongestants, opinion favors administration of pseudoephedrine, which has the most favorable therapeutic index, to reduce potential cardiovascular adverse reactions in the fetus. Intranasal administration of the newer corticosteroids, which have limited absorption, is useful for suppression of allergic rhinitis, while minimizing the risk of adverse reactions. The purpose of this article has been to provide pharmacologic/toxicologic information about commonly used respiratory drugs. This will to enable the clinician to make an educated decision regarding the choice of therapy for respiratory disorders to ensure that fetal and maternal outcomes are optimal.