FITC-inulin is synthesized by reacting fluoresceinyl isothiocyanate (FITC-single isomer) with inulin (from dahlia tubers). The product is a yellow powder which is soluble in water. However since inulin tends to form crystalline aggregates, it is often necessary to heat the solution up to 60 degrees C to achieve complete solubility. Dilute solutions will remain clear on standing but concentrated (10%) may form crystalline precipitates. The molecular weight as determined by Size Exclusion Chromatography calibrated with dextran standards is approximately 5000. Since dextran and inulin have different hydrodynamic volumes, this value is not absolute.