The following technic, based on the patent blue V hemoglobin reaction, is useful for identifying hemoglobin in tissue fixed in neutral formaldehyde solution and embedded in paraffin: Stain the deparaffinized, hydrated sections 3 to 5 minutes in the working reagent, prepared by adding 2 ml. of glacial acetic acid and 1 ml. of 3% hydrogen peroxide to 10 ml. of the filtered stock solution (1 g. patent blue, 10 g. zinc powder, and 2 ml. glacial acetic acid). Counterstain 30 to 60 seconds in 1:1000 safranin solution in 1% acetic acid, rinse, dehydrate with alcohols, clear in xylene and mount in clarite. Total time required, 37 minutes. Blood and tissue and smears may be stained, following fixation in methyl alcohol, by applying the working reagent as above.