Steinach played a significant role in discovering the relationship between sex hormones (estrogen and testosterone) and human physical identifiers.

[5] The testes secretion, now known as testosterone, resulted in the female guinea pig developing male sexual behaviour such as mounting the partner.

[1] Indeed this experimental science was then in its infancy in Vienna and developed over a period of 20 years with incomplete human experimentation, before two members of Hirschfeld's Institut für Sexualwissenschaft (Ludwig Levy-Lenz and Felix Abraham) carried out the first complete male-to-female gender reassignment surgery on a German subject, Dora Richter in 1931.

[14] Harry Benjamin, in a June 1944 obituary for his colleague, attributed the melancholy of his final years to his enforced exile in Zürich and the ‘unjust criticism’ of his rejuvenations and emphasised the ‘enormous impetus’ his work had for biochemists to concern themselves with all the endocrine glands.

[15] Aldous Huxley's 1923 book Antic Hay makes mention of "a fifteen-year-old monkey, rejuvenated by the Steinach process.