A blood-filled sand fly, Palaeomyia burmitis, was recently described from Early Cretaceous Burmese amber. Within the alimentary canal of this sand fly were the amastigotes and promastigotes of a digenetic leishmanial trypanosomatid. Inside the lumen of the thoracic midgut of the fossil sand fly were nucleated blood cells, some of which were intact and others in various stages of lysis and disintegration. The present study identifies these blood cells as reptilian and describes putative developing amastigotes inside spherical to oval whitish vacuoles within some of the fossil blood cells. The significance of this find is discussed, especially regarding the high possibility that Cretaceous dinosaurs were infected by trypanosomatids.