1) The small amount of diacetyl in milk products was microdetermined by the gravimetric method (Nickel salt mothod) and colorimetric method (modified creatine test). It was found that colorimetric method had better result in this determination, because of the sensibility and simplicity.
2) Diacetyl contents in butter, cream and butter milk were 0.22 to 0.29, 0.183 to 7.0, and 0.38 p. p. m. respectively.
3) Diluted solution of synthetic diacetyl smelled of butter. Therefore we think that diacetyl is one of the factors of butter flavor.