Lancet. disease has a slowly developing course, but there is no immunological test with 100% sensitivity to detect antibodies against the parasite. In different series of patients, from 3 to 40% of human hydatidosis cases are found to be seronegative (5). These Difloxacin HCl negative reactions are more frequent when the cysts are located in the lung and brain or in those cysts with hyaline or calcified walls (3, 16). The gold standard immunological test would be one which could detect early on the complete resolution of the Difloxacin HCl disease after medical or surgical treatment. Many attempts have been made to assess complete resolution of the disease after adequate therapy by immunological methods. Detection of serum antibodies, circulating antigen, and circulating immune complexes has been reported to be of potential use in monitoring cystic echinococcosis patients after surgical and chemotherapeutic treatments. Classical immunological tests can be positive for a long time after the surgical eradication of all of the hydatid cysts. Only when a progressive decrease in antibody titers could be detected would the supposition of complete healing appear to be more feasible. Complement fixation and indirect immunofluorescence are the classical tests that more quickly become negative after complete resolution of hydatid cysts, but the results are inconsistent, and, in different revisions, there have been positive results with these immunological tests more than 10 years after curative treatment (4, 7, 12, 14, IL9R 22, 23, 28C30, 32). The main subject of this paper is use of the serological pattern obtained by enzyme-linked immunoelectrotransfer blotting (EITB) in order to improve the sensitivity of this procedure for the diagnosis of hydatid cyst relapse, differentiating the serological patterns of patients with active hydatid disease from those of patients who had had hydatid Difloxacin HCl cysts but who were successfully Difloxacin HCl treated by surgical methods. Second, the effect of the time elapsed after surgery on the accuracy of the prediction of the relapses by serological patterns was studied. For these purposes, a discriminant analysis of the bands obtained by EITB, a sensitive and specific method to diagnose hydatid disease (8, 13, 14, 25, 27, 31), and of conventional serology results was performed in order to detect relapses with a good sensitivity and specificity. The usefulness of this procedure to enhance EITB resolution in the diagnosis of hydatid disease has been described earlier (8). MATERIALS AND METHODS Patients studied. Sixty-eight patients were included in the study and were separated into the following groups. Group 1 consisted of 25 patients with active hydatid cysts. Twenty-two of them had fertile hepatic cysts. One patient had a meningeal relapse. Sixteen patients had newly diagnosed cysts, and seven corresponded to postsurgical relapses. Group 2 consisted of 45 patients with a past history of hydatidosis who were cured by surgical treatment and who did not have any sign of active hydatidosis at the time of the study. Thirty-four of them had been treated 3 years or more before this study (group 2.1), and 11 had been treated within the previous 3 years (group 2.2). Sensitivity and specificity studies of each test, conventional or EITB, for the diagnosis of hydatid disease, including control sera of patients without any history of hydatid disease and sera from patients with parasitosis other Difloxacin HCl than hydatidosis, had been performed and published earlier (8). For all patients a chest X ray and abdominal ultrasonography.