Menopausal hot flushes may be due either to a fall in oestrogen or to an increase in gonadotrophin production. The latter seems the more likely. Paget, Walpole & Richardson (1961) and Brown (1963) concluded from their investigations that 1-α-methylallylthiocarbamoyl-2-methyl-carbamoylhydrazine (dithiocarbamoylhydrazine, (ICI 33828) inhibits gonadotrophin production in animals. Bell, Brown, Fotherby, Loraine & Robson, (1962) and Brown, Crooks, Klopper, Thorburn & Tulloch (1963) demonstrated a reduction in gonadotrophin excretion in post-menopausal women treated with ICI 33828. Bell, Brown, Fotherby & Loraine (1962), using rather low doses of this drug in menstruating women, found no reduction, but the excretion of oestrogens and of pregnanediol was diminished. It seems unlikely that any further reduction in oestrogen production after the menopause could be responsible for the disappearance of hot flushes. If hot flushes were to be reduced by ICI 33828, this would more likely be accounted for by a reduction in gonadotrophin levels.