An enzyme-linked immunoelectrotransfer blot (EITB) for ovine echinococcosis was evaluated in an endemic area of the Peruvian central sierra. An overall test sensitivity of 91.4% was determined for 199 sheep. EITB sensitivity reached a plateau of nearly 100% at 3 years of age, while the prevalence of cystic disease peaked at 95% in sheep ≥6 years of age. In this highly endemic area, 61.7% of sheep without detectable cystic disease at necropsy (n=47) had positive EITB results. Relationships between EITB sensitivity, age, and cyst location, size, number, type, fertility, and viability were evaluated with logistic regression models. EITB sensitivity increased 14-fold in sheep with calcified cysts and 4-fold for each 1cm increase in pulmonary cyst size. © 2003 Elsevier Science B.V. All rights reserved.