Allergic rhinitis is a common health problem affecting about 500 million people worldwide; its prevalence is increasing. The symptoms of allergic rhinitis include sneezing, and an itchy, runny and blocked nose. Several classes of drugs are used to treat allergic rhinitis, but these drugs may be ineffective, and some drug classes have side effects after long-term use. Drugs may also be relatively expensive. Helminths are complex multicellular organisms that inhabit larger organisms, and in humans are often symptomless. Helminths modulate (that is, optimally adjust) the immune systems of their hosts and it is thought that this property of helminths could be used therapeutically, to prevent or treat allergic diseases, such as allergic rhinitis. We included two well-designed studies with a total of 130 adult participants, each study using a different species of gastrointestinal helminth (human hookworm in one study and pig whipworm in the other) as the intervention. Both studies found no significant efficacy from helminths, although one helminth species (Trichuris suis, the pig whipworm) reduced the need for participants to take tablets as rescue medication during the grass pollen season. Adverse events such as abdominal pain and flatulence were commoner in the helminth group, but the two helminths species studied did not cause serious adverse reactions. Currently there is insufficient evidence to support the use of helminths for allergic rhinitis in routine clinical practice. More preclinical studies are needed, before larger and extended duration clinical trials of helminths for allergic rhinitis are performed.