SummaryRaised levels of serum immunoglobulin E are found in many parasitic diseases. In order to determine the influence ofGiardia lambliaon IgE levels of clinically symptomatic patients, a controlled study was performed. There was no difference between the serum IgE values from Brazilian patients with giardiasis and those from normal Brazilian controls, although in both groups there were many individuals with values higher than the normal range reported from the northern hemisphere.