Displacing the physiological model that had held sway in 19th-century medical thinking, early 20th-century medical scientists working on hormones promoted a new understanding of the body, psychological reactions, and the sexual instinct, arguing that each were fundamentally malleable. Hormones came to be understood as the chemical messengers that regulated an individual's growth and sexual development, and sexologists interested in this area focused primarily on children and adolescents. Hormone research also promoted a view of the body in which ‘hermaphroditism’, homosexuality, and (...) ‘sexual perversions’ such as masochism and sadism were attributed to anomalies in the internal secretions produced by the testes or the ovaries. This article focuses on Spanish, Italian, Argentinian, and Brazilian sexology shaped by endocrinological research in the interwar period. First, it shows the key role hormone treatments played in the historical development of sexology in Southern Europe and Latin America. Second, it looks at how sexologists employed hormone research to study human sexual development in the early stages of life, and how they set about ‘correcting’ what they viewed as ‘sexual anomalies’. (shrink)