Posttherapy evaluation of strongyloidiasis is frequently difficult because coprologic examination is not sensitive enough for diagnosis of chronic infection. In the present study, anti-Strongyloides enzyme-linked immunosorbent assay antibodies were monitored before and after treatment with thiabendazole and pyrvinium pamoate in 199 patients with chronic strongyloidiasis in Okinawa, Japan. A significant decrease in antibody levels was observed in patients who became negative for fecal larvae after the treatment, whereas the antibody levels did not show a significant change after the treatment in patients who were still harboring the parasite. In the group coprologically negative in the follow-up examination, however, many individuals did not show a significant fall in antibody titers after treatment, which suggests that these cases were equivocal for complete cure. By the subsequent fecal reexamination performed on the equivocal cases, approximately 20% were additionally found to be still harboring the parasite. These results indicate that serologic testing is useful to check whether a real cure has been achieved among the patients in whose fecal samples the presence of larvae has not been demonstrated after treatment.