A hormone made by a gene called "kiss" has the potential to restore fertility in some women, scientists have found.
Twice-weekly injections of the natural drug lead to long-term increases in levels of sex hormones that control the menstrual cycle, a study showed.
The findings suggest a new way to treat women whose infertility is due to low sex hormones.
Kiss-1 is a gene that plays a key role in regulating reproduction. It produces the hormone kisspeptin, which helps humans and other animals go through puberty and become sexually mature.
Researchers from Imperial College London led by Dr Waljit Dhillo studied a condition called hypothalamic amenorrhoea, which prevents menstruation and causes infertility.
Several thousand women in the UK are affected by the hormonal disorder each year.
Over a period of eight weeks, a group of 10 infertile women with hypothalamic amenorrhoea were given twice-weekly injections of either kisspeptin or a salt solution.
Blood samples were taken to measure their levels of luteinising hormone and follicle stimulation hormone, both of which are essential for ovulation and fertility.
Women experienced a large increase in the circulating sex hormones at the start of the treatment, which halved by day 14. However, after two weeks, their responsiveness to kisspeptin remained steady.
On the last day of the trial, the hormonal responses of women given kisspeptin injections were 16 times higher than those of women who received the salt treatment.
The findings were presented yesterday at the Society for Endocrinology BES meeting in Manchester.
Dr Dhillo said: "Infertility is a highly distressing condition. The results of our study are exciting as they show that kisspeptin may be a novel method for restoring fertility to women with certain types of infertility.
"Our findings show that an injection of kisspeptin given twice weekly can reinvigorate the reproductive hormone system in women and raise their levels of luteinising hormone and follicle stimulating hormone, both of which are essential for fertility.
"This is only a small study and we need to carry out further work before our findings can be brought into clinical practice," he added.