Using parasite agglutination, indirect immunofluorescence, enzyme-linked immunosorbent assay, and immunoblotting, Giardia lamblia specific antibody was detected in 5 commercially available immunoglobulin (IgG) preparations. IgG antibodies to Entamoeba histolytica were either present in very low titre or were absent. Immunoblotting showed that anti-G. lamblia antibodies were detected towards a range of Giardia proteins, 25-200 kDa. These findings raise the possibility that pooled human IgG preparations could be evaluated in the treatment of chronic giardiasis which is refractory to conventional therapy.