Scientists at King's College London have announced the creation of the first line of human embryonic stem cells in the UK. BBC News Online looks at the scientific, legal and ethical implications.
Human stem cell lines were first created from embryos longer than four years ago. Why has it taken so long to happen in the UK?
Research work on human embryos is regulated by the Human Fertilisation and Embryology Authority.
It did not grant licences for the work to go ahead until 2002.
The move followed a House of Lords recommendation that the work be allowed to proceed.
Why do scientists want to create these cell lines?
Stem cells are undifferentiated, that is to say that they have the potential to become virtually any kind of cell in the body.
The researchers' aim is to learn how to control this differentiation process so that large quantities of cells can be grown for transplant.
Sufferers of Parkinson's disease could benefit from transplants of dopamine-producing cells and diabetics could benefit from transplants of insulin-producing cells, the scientists believe.
Which other conditions could be tackled?
Some cancer researchers are enthusiastic about stem cell research because they hope to replace cancer-damaged tissues.
Alzheimer's disease is another condition where diseased cells might be replaced by transplanted ones.
And heart disease is something which might be dealt with by some form of cell transplantation.
Is there no alternative to taking cells from human embryos?
Stem cells can also be derived from cells taken from an adult.
Scientists using this method seek to persuade the cell to "forget" its current status and go back to the original stem cell state it was in during its time in the embryo.
Groups opposed to stem cell work on embryos say the use of embryos is immoral and unnecessary, because the procedure destroys the embryo and because an alternative is available.
Scientists working on embryos say that stem cell research is in its infancy and not enough is known about the potential of either adult or embryonic stem cells to abandon one approach in favour of the other.
They say the embryos they use are left over at the end of IVF treatment and would have had to have been destroyed in any case.
UK legislation requires that unimplanted frozen embryos created for IVF be destroyed after five years.
At the point at which the embryos are destroyed, a few days' development has taken place since fertilisation and they are a microscopic clump of cells.
What will the scientists do next?
Successful treatments are still a long way off. Scientists do not yet fully understand how to guide the process of differentiation to produce useful amounts of particular types of cell.
The research they are carrying out now is aimed at developing techniques to control cell differentiation.
They will also deposit some of the cells they have cultivated into a cell bank so that other researchers may use them.
Cells from one single embryo will end up used by several different teams of researchers working on different applications.