One intramuscular injection of biosynthetic human growth hormone (24 IU), administered on the first day of gonadotrophin treatment for ovulation induction, significantly augmented the ovarian response to gonadotrophic stimulation in seven patients. Compared with a protocol involving six injections of 24 IU of GH given on alternate days to the same patients, the smaller dose had an intermediate but highly significant effect in reducing the amount, duration of treatment and daily effective dose of hMG needed to induce ovulation. The difference between the effect of the one-dose and six-dose protocols was small. The action of growth hormone on the human ovary, probably mediated by insulin-like growth factor-1 (IGF-1), appears effective in enhancing the response to gonadotrophin therapy even when given in a single dose.