Marsh harriers and other raptors may become poisoned by ingesting lead gunshot in the flesh of their prey. Blood lead is a suitable indicator of exposure to lead. The method usually used in our laboratory for the analysis of human blood induced coagulation of avian blood. In this paper we report upon the optimization and quality control of a method to determine lead in avian blood samples. Samples were prepared using a diluent and matrix modifier. Analysis was carried out using graphite furnace AAS with a L'vov platform and Zeeman-effect background correction. The method was validated using international intercalibration comparisons of lead in human blood. The method proved to have a high degree of sensitivity, reproducibility and accuracy. The detection limit was low (0.004 ppm). The method used is discussed in relation to those previously used for lead analysis in avian blood. Keywords: lead, avain blood, Circus aeruginosus, graphite furnace AAS, matrix modifier.