In October, 1913, the receipt of a sample of blue milk by the dairy section of the Iowa Agricultural Experiment Station prompted an investigation of this uncommon phenomenon. Careful study of the organism involved proved it to be Bac. cyanogenes, the same organism that has been isolated in other instances of blue milk. As far as is known, this organism is entirely harmless and milk which is turned blue by it is objectionable only on account of its color.