Abstract: The reaction product obtained from the condensation of sulfanilamide and guanidine nitrate in the presence of sodium carbonate is a yellowish-gray, hygroscopic powder,containing 10 to 12 per cent of sulfanilamide and 40 to 45 per cent of sulfaguanidine. A quantitative method is described for the separate determination of the two constituents.It is based upon the different solubility of sulfanilamide and sulfaguani- dine in 5 per cent solution of sodium hydroxide,in which,sulfanilamide is freely soluble and sulfaguanidine is but very slightly soluble.Other impurities present in the reaction product were found to be not interfering with the determination. The method is rapid,the time required for the parallel determination being not more than 70 minutes with an error of about 0.2 per cent.