Identification of microg. quanti-ties of histamine in blood was accomplished by means of a simple extraction procedure followed by partition chromatography. An otherwise nonspecific color reaction employing P-bromoaniline is thus rendered specific. A min. of approxi-mately 3 microg. of histamine in 20 ml. or more of blood can be identified. Rough quantitative estimation is feasible. The method was employed to identify histamine as released in ana-phylactic reactions.