The effect of 3 different detergents (Triton X-100, Lubrol WX and Nonidet) on brain thromboplastin was examined and compared with the solubilisation due to deoxycholate. The effect of deoxycholate is superior over that of the other examined detergents. Deoxycholate extracts thromboplastic activity from brain tissue to a large extent. Furthermore it has no interfering absorbance at 280 nm. The aminopeptidase of brain tissue may be separated from thromboplastin. It does not have any coagulation activity.