Recently, a 'new' filarial syndrome has been described as one of clinical and immunologic hyper-responsiveness found in expatriate visitors to regions endemic for loiasis. This clinical syndrome is, of course, not new, nor is it limited to loiasis (tropical eye worm), as similar clinical descriptions of patients with onchocerciasis, lymphatic filariasis, and other filarial infections also have been recorded previously. Instead of developing the commonly described chronic clinical manifestations of their filarial infections, individuals who have grown up outside endemic regions and then moved to these regions and acquired a filarial infection manifest prominent signs and symptoms of inflammatory (including allergic) reactions to the mature or maturing parasites. In loiasis, these manifestations have included primarily Calabar swellings, hives, rashes and occasionally asthma; and in bancroftian filariasis (when military personnel or other migrants to endemic areas have acquired these infections), symptoms have usually been lymphangitis, lymphadenitis, genital pain (from inflammation of the associated lymphatics), along with hives, rashes and other 'allergic-like' manifestations, including blood eosinophilia. The reason for these different clinical presentations lies almost certainly in the different immunoregulatory responses to filarial antigens between those with long (including prenatal) exposure to these antigens and those meeting them for the first time.