Total and specific serum IgE antibodies were estimated in a 68-year-old woman with anaphylactic shock due to spontaneous rupture of hydatid cyst of the liver. After she had recovered, an abdominal ultrasonography showed a cyst, 10 x 15 cm, in the right hepatic lobe. The cyst was surgically removed. Antihydatid IgE in the acute phase and periodically after surgical intervention, determined by Phadezym RAST, Pharmacia, and Pharmacia CAP system (a new solid-phase immunoassay, fully automated, for the titration of specific IgE with greater sensitivity in the detection of low IgE antibody levels), showed decreasing antihydatid IgE antibodies on day 10 after surgical intervention and may thus serve to monitor the evolution of hydatid disease.