Diagnosis of fasciolosis in the acute phase depends on a sensitive and accurate serological test. The present study is an evaluation of the efficacy of excretory-secretory Fasciola gigantica adult worm antigen by IgM ELISA. Thirty eight patients with acute fasciolosis and 14 in the chronic phase together with 23 patients with different parasitic infections were introduced in the study. Seventeen healthy, parasite free individuals, were served as controls. A crude excretory-secretory antigen and its fractions I and II (obtained by gel filtration chromatography on Sephadex G-200) were tested. The crude antigen revealed 100% sensitivity, 94% specificity and 98% accuracy at the cut off level of 0.3 in acute infection. It gave positive results in 77% of chronic cases. Cross reactions with Schistosoma and Toxoplasma were negligible. A significant positive correlation between IHA titres and ELISA O.D. readings was observed. Fractions I and II proved of no diagnostic significance. The test system F. gigantica E/S product by IgM ELISA is highly recommended for diagnosis of acute fasciolosis.