A method that can generate human embryonic stem cells without harming embryos? In August biotechnology firm Advanced Cell Technology (ACT) in Worcester, Mass., claimed it had developed just such a procedure. The company touted it as a way around the firestorm of controversy surrounding the conventional technique for growing these cells, which destroys human embryos. Most researchers find the method intriguing, because it might lead to new and maybe better stem cell lines. But several also argue that it raises fresh dilemmas.

Scientists investigate human embryonic stem cells because they can become any other kind of cell. As such, they hold great promise in regenerating body parts. Conventionally, researchers rely on embryos produced during in vitro fertilization (IVF) attempts, removing the inner cell mass from embryos that have grown to 50 to 100 cells. Currently at least 400,000 frozen embryos lie unused in U.S. fertility clinics, and thousands are typically discarded annually.

This article was originally published with the title Blastomere Blowup.

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