It is 23 years since the first test-tube baby was born in Britain from an egg taken from her mother and fertilised outside the womb. Countless times since then, human embryos have been extracted and used in scientific experiments. So far as is known, all this research has been intended for the betterment of mankind.
But is that truly the case? If life is sacred, can it be less sacred in the initial stages? Does an embryo have to develop recognisable human form before it is entitled to protection? Are we perilously close to the point where reproductive science becomes a Frankenstein profession?
The biggest moral dilemma to date is one that US President George W. Bush has to decide. American scientists are in the race to provide replacement tissue to cure illnesses such as Parkinson's disease by growing embryos in the laboratory until they develop the necessary stem cells.
Unlike Britain, where the go-ahead was given under strict ethical rules imposed by the Human Fertilisation and Embryology Authority, questions surrounding this research remain divisive in America. The anti-abortion lobby - which Mr Bush supports - is vehemently opposed, though individual senators are wavering, notably those whose family members suffer from conditions that stem cell therapy may one day cure.
The research embryos are so minute that even magnified 20 times they are the size of a grain of pollen. Nothing but a cluster of indeterminate cells, they have yet to divide to form distinct organs. Harvested and injected into sufferers of diabetes, leukaemia, osteo-arthritis or heart and kidney diseases, they have the potential to regenerate damaged tissue.
Scientists at a handful of institutions have already found ways to multiply stem cells in the laboratory without the need to use embryos. Some are universities, others are biomedical companies. That lifts the issue beyond pure research and into the realms of commerce. The team that turns today's promise into reality will reap rich financial awards. Human suffering will be reduced on a massive scale.
Mr Bush, whatever his personal views, risks sidelining the US if he vetoes funding. The reality is that nothing will prevent the research from advancing, however justified the moral arguments. Those who see this as an issue of profound principle cannot compromise. But nor can they save the millions of embryos thrown out at fertility clinics.
However, they may be able to influence events by urging the adoption of stringent ethical rules to ensure research is driven purely by the desire to improve the human condition rather than a race to hit the jackpot first.