Therapeutic use of oestrogens by males with carcinoma of the prostate leads to testicular atrophy with markedly reduced spermatogenesis after only 21 d (Oshima et al. 1974). Treatment for over a year results in paucity of germ cells, vacuolation of Sertoli cells and reduction in Leydig cells (Lu & Steinberger 1978, Smith & Urry 1985). There is, apparently, no information on the histology of the human testis after more than 1 year oestrogen therapy. We here report changes in testes from five transsexuals treated for periods of up to 5.5 years.