Abstract. Follow-up stool examinations were carried out on two groups of the subjects who were screened negative (group 1) or positive (group 2) for Strongyloides stercoralis by the agar plate culture. This technique could detect S. stercoralis larvae in 87.5-96.4% of the subjects in group 2 and 0-5.9% of the subjects in group 1 on various days of the eight-week and four-week follow-up periods, respectively. The detection rate on each day of examination was not statistically different from that on the first day in both groups. Quantitative measurement of S. stercoralis larvae excreted in the feces of the subjects in group 2 by the standard direct smear method of Beaver and others revealed slight to marked fluctuations of the larval output in individual subjects. From the results of both stool examination methods, it could be implied that 52% of S. stercoralis-infected individuals had low-level infection.Strongyloides stercoralis is an intestinal nematode of humans with a rather unique biology in that it has a free-living phase outside the host. Human infections due to S. stercoralis are distributed primarily throughout tropical and subtropical regions of the world. 1 Reports of S. stercoralis infections in non-endemic countries were from the ex-prisoners of the World War II 2,3 or the Southeast Asian immigrants. 4 The clinical spectrum of strongyloidiasis varies from asymptomatic infection, to mild symptomatic abdominal and skin diseases, to fatal disseminated infection in immunosuppressed patients. 5 The reported prevalences of S. stercoralis infection are difficult to ascertain and may have been underestimated because most infections are with low larval densities in the feces.1 They are also difficult to compare because of the difference in the coprologic methods used to detect the larvae. Earlier methods for the diagnosis of S. stercoralis infection such as the simple direct smear and formalin-ether concentration are often unreliable because of their relatively low sensitivity. In recent years, the agar plate culture technique has been introduced and found to give consistently higher sensitivity (78-100%) than simple direct smear (0-52% sensitivity) and formalin-ether concentration method (13-55% sensitivity). 6-10 Several immunologic methods have also been used in the diagnosis of strongyloidiasis. Currently, the most widely used method has been the ELISA using crude antigen extracts of filariform larvae as antigens. Most reports on the ELISA for strongyloidiasis have shown consistently high sensitivity, but the specificity has varied widely due to different criteria used for the selection of uninfected individuals. [11][12][13][14][15][16] Recently, Western blot analysis has been applied to the immunodiagnosis of strongyloidiasis. Preliminary data have indicated that immunodominant proteins (apparent molecular weights of 41, 31, and 28 kD) of S. stercoralis filariform larvae are recognized by strongyloidiasis sera with high sensitivity and specificity. [17][18][19] It is generally known that the detection o...