[Laboratory diagnosis of pregnancy begins: Abderhalden's test].

The first decades of the twentieth century were the times of intensive search for a reliable laboratory test for early pregnancy. Among some tests proposed, the one developed in 1912 by a Swiss pioneer in clinical biochemistry, Emil Abderhalden, earned greatest response. Unlike other authors of pregnancy tests, Abderhalden claimed that his "defense ferments reaction" (Abwehrfermentsreaktion), if performed according to his methodology, was 100% specific and sensitive for pregnancy, even in its first weeks. Abderhalden's test raised much interest worldwide. Within the first few years from its first announcement, several hundred papers on the evaluation of the test's reliability were published, most of them enthusiastic. Variations of Abderhalden's test were hoped to work effectively as diagnostic tools in psychiatry, oncology, and internal diseases. Many clinicians believed that thanks to Abdehalden's method a wide range of conditions, such as schizophrenia, depression or cancers, could be unequivocally diagnosed with one serum test. In 1928, Abderhalden's reaction as a pregnancy test was replaced with the biological test developed by Aschheim and Zondek. In psychiatry, however, Abderhalden's test was used and evaluated as a diagnostic tool up till the 1930s. Only after Abderhalden's death in 1950 the "defense ferments reaction" was finally rejected as having no reliable scientific background. This paper presents the circumstances in which Emil Abderhalden developed his diagnostic test, the principles of the test, the methodology proposed by Abderhalden, as well as the response to the test and its variations in Germany and other countries.