Walter Siegfried Loewe was born on August 19, 1884, in Fürth, Bavaria. The centenary of his birth should be of interest to pharmacologists, endocrinologists and clinical chemists, alike. In this short review an attempt has been made to describe the contributions of Loewe and his coworkers to the biochemistry and analysis of the sex hormones. Loewe began his research on dose effect-response of ovarian extracts at the University of Dorpat, Estonia. By quantification of the Allen-Doisy-test, Loewe was the first to succeed in measuring oestrogens in human blood and urine. Further scientific research was focussed on the content and the local effects of oestrogens within the placenta. In the same time, Loewe and his coworker Voss developed the first, specific bioassay for the male hormone. It was based on the histological repair of the epithelium of the seminal vesicles in castrated mice, brought about by the injection of testicle extracts. With the aid of this so-called "cytological regeneration test" Loewe was able to isolate and characterize androgens from different biological sources. The male hormone was called "androkinin", and in 1928 Loewe reported the occurrence of androkinin in human male urine and its separation from oestrogens in the same material. On the basis of the early mitogenic effect of androgens the bioassay of Loewe & Voss was further improved, serving as a fundamental prerequisite for the isolation and chemical charcterization of the androgens in the early thirties. Loewe who had held the chair of pharmacology at Dorpat since 1921, came to Mannheim in 1928 as head of the Main Laboratory of the Municipal Hospital. In 1933 he was forced to emigrate, went first to Cornell-University, New York and later to the Department of Pharmacology at the University of Utah. In 1948 he became an honorary member of the German Pharmacological Society and in 1960 of the German Society of Endocrinology. Three years later, on August 24, 1963 at Salt Lake City, Loewe died at the age of 79 years.