Loiasis in residents of endemic areas is generally manifested by microfilaremia, episodic angioedema, periocular migration of adult worms, modest eosinophilia, and variable antibody levels. In 20 temporary residents who acquired loiasis in West Africa, however, the clinical presentations were markedly different. Only three of the 20 had detectable microfilaremia. Furthermore, these patients often showed a state of marked immunological hyperresponsiveness manifested by very high titers of antibody to filariae, increased levels of serum IgE, and profound hypereosinophilia--to levels greater than 3,000/mm3 in 18 of the 20. These patients were also notable for the increased severity, frequency, and pruritic nature of their angioedema. Also, significant complications occurred in seven of the 20; one patient developed endomyocardial fibrosis and six, renal disease after treatment with diethylcarbamazine. Thirteen of the 20 developed subcutaneous nodules; adult parasites were recovered from three of five of these patients who underwent biopsy. All of the patients responded to therapy with diminution of their clinical symptoms and decreases in levels of eosinophils, IgE, and antibody to filariae.