The use of a new immunoassay, time-resolved fluoroimmunoassay (TR-FIA), in the diagnosis of human hydatid disease has been evaluated. This technique, which is based on the labelling of antibodies with europium (Eu), was compared with a well-established method, the enzyme linked immunosorbent assay (ELISA). Of 102 patients with hydatid disease, 97 (95.1%) were positive according to TR-FIA and 83 (81.4%) according to ELISA. The rate of non-specificity for other parasitic infections (n = 206) was 8.7% for TR-FIA and 17.5% for ELISA. It is concluded that TR-FIA is more sensitive and more specific than ELISA in the diagnosis of human hydatid disease.