Aims: Characterization of the representative protozoan Acanthamoeba polyphaga surface carbohydrate exposure by a novel combination of flow cytometry and ligand - receptor analysis. Methods and Results: Trophozoite and cyst morphological forms were exposed to a panel of FITC - lectins. Population fluorescence associated with FITC - lectin binding to acanthamoebal surface moieties was ascertained by flow cytometry. Increasing concentrations of representative FITC - lectins, saturation binding and determination of K-d and relative B-max values were employed to characterize carbohydrate residue exposure. FITC - lectins specific for N-acetylglucosamine, N-acetylgalactosamine and mannose/glucose were readily bound by trophozoite and cyst surfaces. Minor incremental increases in FITC - lectin concentration resulted in significant differences in surface fluorescence intensity and supported the calculation of ligand-binding determinants, Kd and relative Bmax, which gave a trophozoite and cyst rank order of lectin affinity and surface receptor presence. Conclusions: Trophozoites and cysts expose similar surface carbohydrate residues, foremost amongst which is N-acetylglucosamine, in varying orientation and availability. Significance and Impact of the Study: The outlined versatile combination of flow cytometry and ligand receptor analysis allowed the characterization of surface carbohydrate exposure by protozoan morphological forms and in turn will support a valid comparison of carbohydrate exposure by other single-cell protozoa and eucaryotic microbes analysed in the same manner.