Purpose.Exposure toAcanthamoebaspecies appears to be ubiquitous, as 50% to 100% of healthy human subjects display anti-Acanthamoebaantibodies. However, the presence of specific anti-Acanthamoebaantibodies in the serum and tears of patients has not been investigated. The prevalence of serum immunoglobulin G (IgG) and tear IgA against three species ofAcanthamoebawas assessed in healthy subjects and patients withAcanthamoebakeratitis.Methods.The level of specific serum IgG and tear IgA againstA. castellanii,A. astronyxis, andA. culbertsoniin the sera of 23 patients and 25 healthy subjects was tested by enzyme-linked immunosorbent assays. Total serum IgM, IgG, and IgA concentrations were measured by nephelometry.Acanthamoebakeratitis was diagnosed clinically and confirmed by in vivo confocal microscopy. In some patients, corneal biopsies were also performed and trophozoites were cultured on lawns ofEscherichia colion non-nutrient agar.Results.All healthy subjects and patients withAcanthamoebakeratitis had detectable serum IgG antibodies against allAcanthamoebaantigens. However, patients withAcanthamoebakeratitis had significantly higher anti-AcanthamoebaIgG antibody titers than healthy subjects. In contrast,Acanthamoeba-specific tear IgA was significantly lower in patients withAcanthamoebakeratitis in comparison with healthy subjects. Total serum immunoglobulins did not differ significantly between healthy subjects and patients withAcanthamoebakeratitis.Conclusions.The results suggest that a low level of anti-AcanthamoebaIgA antibody in the tears appears to be associated withAcanthamoebakeratitis.