SummaryThe ratio of stippled cells, observed on dark field after staining by methylen blue, has been found higher in patients with thyreotoxicosis (4.000 to 40.000) per million) than in normal subjects (0 to 3.000) per million). Stippled cells are not produced by direct action of toxic substances. They are probably in relation with an excitation of the erythropoïetic system. They are not identical to the reticulocytes. Perhaps they provide us with a new possibility for the diagnosis of thyreotoxicosis.