To review which herbs are most commonly used as complementary and alternative medicine (CAM) for treatment of asthma, allergy, and immunologic conditions. A review of the literature was performed using the PubMed and OVID databases searching the keywords asthma, allergy, and CAM to identify studies published between 1980 and 2003 that focused on Echinacea (Echinacea augustifolia, Echinacea pallida, and Echinacea purpurea); garlic (Allium); angelica; chamomile; ephedra; gingko; grape seed extract; licorice root (Glycyrrhiza); St. John's wort (Hypericum); kava kava (Piper); peppermint oil and leaf (Mentha); stinging nettle (Urtica); and ginseng (Panax) published in the English and German literature. Studies included in vitro and in vivo clinical trials and case reports selected according to the expert opinion of the author. Echinacea is one of the most common herbs used to treat symptoms of the "common cold" or upper respiratory tract allergies. Although no common drug interactions have been reported, there is a risk of hepatotoxicity, exacerbation of allergies and asthma, and anaphylactic reactions. Garlic is primarily used for cardiovascular health and relief of cough, colds, and rhinitis. Adverse effects commonly include gastrointestinal disturbances, change in body odor through the sweat and breath, and rarely allergic reactions or hypoglycemia. Other CAM agents, including angelica, German chamomile flower, ephedra, gingko, grape seed extract, licorice root, St. John's wort, kava kava rhizome, peppermint, stinging nettle, and ginseng, are also associated with significant adverse effects. The specialty of allergy and immunology has seen the second largest increase in the popularity of CAM (second only to practitioners who treat lower back pain). Almost all of the CAM interventions have displayed adverse effects, usually in the form of a hypersensitivity reaction. Allergists and clinical immunologists need to become more knowledgeable about CAM so that they can inform patients about the use and possible abuse of these modalities.