Thirty cystic echinococcosis (CE) patients in Uruguay with severe bone or secondary disseminated echinococcosis were immunologically assessed using cellular (lymphocyte transformation assay, LTA) and humoral (specific antibody and subclass responses, circulating antigen and circulating immune-complexes) immunological assays during the course of chemotherapy (albendazole and/or praziquantel). CE patients were divided into 4 groups, according to clinical treatment and outcome: (I) surgery and chemotherapy, (II) chemotherapy with outcome unchanged, (III) chemotherapy with outcome improved, and (IV) chemotherapy considered cured. Increased circulating antigen was of prognostic value in some severe CE cases where levels remained high and/or increased. The lymphoproliferative response in vitro to Echinococcus granulosus antigen was statistically greater in all patient groups compared to normal individuals but at lower levels in improved or cured CE patients. Levels of non-specific LTA response were significantly lower than controls for all groups during albendazole treatment (P < 0.001) but returned to normal levels in cured patients, a result consistent with parasite-induced suppression of cellular responses. This study suggests that, at least in severe osseous and secondary CE, immunosurveillance by specific antibodies, especially total specific immunoglobulin, was overall of more practical use than antigen-specific in-vitro lymphocyte transformation assays.