SUMMARY. A flow cytometry method for quantifying levels of anti-D is described. The method is based on the indirect antiglobulin test and uses an FITC Fab anti-human IgG reagent for detection of bound anti-D. A standard curve is generated from the fluorescence measured by flow cytometry using the British Standard anti-D preparation 73/515. The fluorescence obtained from test samples by flow cytometry is converted into IU/mL anti-D, using the standard curve. In a limited study with 42 serum samples the assay showed good correlation with results obtained using the AutoAnalyser for sera with anti-D levels less than 100 IU/mL. The method is simple to perform and has potential as a replacement for the AutoAnalyser.