Giardia lamblia is one of the most common causative agents of diarrhealillness throughout the world and Egypt. The importance of accuratediagnosis of patients with chronic giardiasis lies in the fact that childrenmay suffer from elongated periods of profound malaise, diffuse epigastricpain, abdominal discomfort and malabsorption. For laboratory diagnosis,the most utilized method is microscopic examination of fecal samples, butthe immunoenzymatic method is also available. The aim of this work wasto verify the advantages and drawbacks of immunoassaying versusmicroscopy for diagnosing G. lamblia, when a single fecal sample isanalyzed.Samples were examined using direct wet smear, formol etherconcentration technique and ELISA. The ProspecT ELISA kit was usedfor detecting G. lamblia-specific antigen (GSA-65), in accordance withthe manufacturer's instructions. Results were expressed by bothspectrophotometry and visual scale.Results: The ELISA test was positive even when a significant proportionof corresponding samples examined by microscopy were negative. Thistrend was statistically significant (p < 0.001).Conclusion: There is an increasing demand for diagnostic testing for G.lamblia with a priority being placed on obtaining results in an efficientand timely manner. The ELISA test is of great benefit in chronicmisdiagnosed cases. When comparing test costs, all aspects should beconsidered. The high morbidity and ineffective empirical treatment thataccompanies misdiagnosis, ultimately lead to higher cost on the healthcare sector and the whole community.