Two species of imported fire ants (IFA) now infest large areas of the southern United States. The most aggressive species, Solenopsis invicta, has adapted well to environmental conditions in the south where it has become a considerable agricultural pest and a significant public health problem. Sting reactions range from local pustules and large, late-phase responses to life-threatening anaphylaxis. Four important Sol i venom allergens have been isolated and characterized. Clinical studies under way are designed to compare the safety and efficacy of fire ant venom (IFAV) with IFA whole body extract (WBE) for diagnosis and treatment of fire ant allergy.