Hereditary angioedema (HAE) is an autosomal dominant disease associated with episodic attacks of nonpitting edema that may affect any external or mucosal body surface. Attacks most often affect the extremities, causing local swelling, the GI tract, leading to severe abdominal pain, and the mouth and throat, at times causing asphyxiation. Most patients with HAE have low levels of the plasma serine protease inhibitor C1 inhibitor. The edema in these patients is caused by unregulated generation of bradykinin. Effective chronic therapy of patients with impeded androgens or plasmin inhibitors has been available for decades, but in the United States, we do not have therapy for acute attacks. Five companies have completed or are in the process of conducting phase 3 clinical trials, double-blind, placebo-controlled studies of products designed to terminate acute attacks or to be used in prophylaxis. Two companies, Lev Pharmaceuticals and CSL Behring, have preparations of C1 inhibitor purified from plasma that have been used in Europe for decades (trade names Cinryze and Berinert P, respectively). One company, Pharming, has developed a recombinant C1 inhibitor preparation. One company, Dyax, is testing a kallikrein inhibitor (ecallantide), and one company, Jerini, is completing testing of a bradykinin type 2 receptor antagonist (Icatibant). Although little has been published thus far, all of these products may prove effective. It is likely that HAE treatment will change dramatically within the next few years.