In the reducing environment of anoxic basins manganese (III) or (IV) is reduced to soluble Mn (II); the deep waters of the Black Sea contain up to 500 µg Mn (II)/ liter, about 100 times the oceanic average. When this manganese was measured with formaldoxime, color development was erratic if the reagents were added separately. Rapid and reproducible color development was achieved by using a mixed ammonia/formal‐doxime reagent added singly to the sample. Precipitation was avoided by maintaining the pH in the range 8.8–8.9. No interferences from sulfide or dissolved salts were observed. A small correction was made for interference due to iron. Dissolved manganese values in the Black Sea ranged from a midwater maximum of ca. 460 µg Mn/liter to ca. 250 µg/ liter in deep water.