A modified counterimmunoelectrophoresis and a conventional indirect hemagglutination test were compared for routine diagnosis of human hydatid disease in an endemic area in the Middle East. Counterimmunoelectrophoresis was performed on a cellulose acetate membrane with dilutions of a commercially available antigen which interacts with sera of patients with confirmed hydatid disease to produce the arc 5 precipitin line. The test was performed with unconcentrated human sera and the lines stained in an aqueous solution of Ponceau red. Sensitivity (95.5% vs. 93.2%) and specificity (99.2% vs. 89.9%) were higher with counterimmunoelectrophoresis than with indirect hemagglutination. Cross-reactivity with sera of patients with other parasitic infections was noted with indirect hemagglutination but not with counterimmunoelectrophoresis. There was no cross-reactivity with sera of patients with autoimmune disorders by either test.