Diagnosis of strongyloidiasis using stool examination remains unsatisfactory due to the lack of sensitivity and fastidious techniques. In this work, we investigated the value of an anti-Strongyloides IgG enzyme immunoassay (EIA), using a panel of 207 sera retrospectively collected from patients with definitive diagnoses of strongyloidiasis (n ؍ 57), other helminthic infections (n ؍ 46), eosinophilia without parasitic infection diagnosis (n ؍ 54), and digestive disturbances following a tropical journey (n ؍ 30) and from 20 negative controls. By following a receiver operating characteristic (ROC) curve analysis, it was possible to optimize the test to reach a sensitivity of 91.2% and a specificity of 93.3%, with 92.8% of patients correctly classified. Considering the incidence of strongyloidiasis diagnosed in our own laboratory, the negative predictive value was calculated at 99.9%. In conclusion, this test is very rapid and easy to perform and may be valuable for diagnosis of strongyloidiasis both in cases where the infection is unrevealed by a parasitological stool examination and in patients at risk for severe clinical forms, such as patients receiving immunosuppressive therapy.Strongyloidiasis is due to the intestinal nematode Strongyloides stercoralis. Due to poor sanitary conditions (lack of latrines) and because warm and moist climates promote the achievement of the life cycle of the parasite, the prevalence of the disease remains high in tropical and subtropical regions of the world (11). Thus, in temperate-climate countries, the infection is almost exclusively seen in patients originating from or having lived in these regions of the world. Usually, strongyloidiasis is responsible for mild abdominal troubles such as pains, alternation of diarrhea, and constipation (15). This infection may also be present with pruritus and crawling sensations under the skin. A peculiar form is the larva currens syndrome, where larvae migrate into the derma. It is considered that the intensity of the symptoms is correlated with the digestive parasitic burden. However, in cases of immunosuppression, such as that induced by human T-cell leukemia virus type 1 (HTLV-1) infection, corticosteroid treatment, or cytotoxic chemotherapy, an uncontrolled life cycle can take place, leading to the so-called hyperinfestation syndrome and even to dissemination of larvae through the body, the latter being associated with a very bleak prognosis (1,5,10,12).Thus, it is essential to diagnose strongyloidiasis in patients coming from areas of endemicity, notably patients with mild or no symptomatic forms, before the initiation of any kind of immunosuppressive treatment. Indeed, the endogenous autoinfection cycle of the parasite promotes the persistence of the parasite for decades, and strongyloidiasis has to be screened for even in cases where the patient stayed in an area of endemicity in the distant past (8). Eosinophilia is indicative of the disease but is frequently mild and nonspecific. To date, diagnosis of strongyloidiasis relies ...