Scientists have been granted permission to screen test tube embryos for an inherited form of cancer.
Embryo screening is already used to detect some other disorders
The Human Fertilisation and Embryology Authority (HFEA) approved the screening following a request from couples seeking IVF treatment.
The watchdog said there was a strong chance of the genetic bowel cancer being passed from parent to child.
Scientists in London hope using the controversial technique could help to wipe out this type of cancer.
A spokeswoman for the authority said: "We can confirm that we have issued a pre-implantation genetic diagnosis licence for that particular condition."
A team at University College London has been granted the licence to screen embryos for the gene that causes familial adenomatous polyposis (FAP).
If a parent is a carrier of the gene there is normally a 50% chance it will be passed on to their children.
The gene can lead to the development of rectal or colon cancer in early teenage years.
Embryos created using IVF can be screened using the pre-implantation genetic diagnosis process.
Then only embryos free of the gene will be implanted.
One of the couples to win the right to have their IVF embryos screened said they were delighted with the decision.
They told The Times newspaper: "We are overjoyed to have been given this chance, not only to do as much as possible to make sure our children don't have the gene,
but to stop them passing it on."
The technique is already used in screening for other disorders such as cystic fibrosis.
But this is thought to be the first time it has been used for a disease that does not affect the sufferer until early adulthood.
Dr Mohammed Tarannisi, director of the Assisted Reproduction and Gynaecology Centre in London, said the latest decision should have been "put to a wider audience".
He told BBC Radio 4's Today programme: "We are still talking here about medical conditions that have serious implications, but we are talking about conditions that are not going to be there at the time of birth.
"These are conditions that may or may not develop 20, 30, 40 years down the line. Is this the right thing to do?
"It is not up to the HFEA or three members of the HFEA or even a clinician like myself to make these kinds of decisions.
"This is an issue that needs to be debated properly."
Dr Tarannisi has an application for a licence to test for breast cancer genes being considered by the HFEA.
Josephine Quintavalle of Comment on Reproductive Ethics said: "It's a very big ethical step forward.
"The HFEA has yet again taken a big ethical decision without consulting the public."
She said it was moving down a slippery slope from what had started as intervention for only disease that threatened the viability of the embryo to diseases that might appear in adulthood.
"We should be looking for medicines that cure not medicines that kill," she said.