In speaking of methods for serodiagnosis of pregnancy, I refer to the biologic tests of Abderhalden only, because the method of Rosenthal, while of considerable scientific interest, appears to be of small practical value. It is applicable during advanced pregnancy only, and all conditions associated with increased destruction of the body proteins respond to the same test. Abderhalden's methods of serodiagnosis of pregnancy, on the other hand, give reliable information just as soon as the ovum is permanently implanted; these methods are based on specific reactions and they are suited for the widest application in the study of physiologic and pathologic conditions. To appreciate the value and the scope of these methods it is essential to have a clear understanding of the underlying principles and to be familiar with the monumental work of Abderhalden on cell metabolism and on protective ferments, which covers a period of more than ten years