On p. 1669 of this issue of Science appears the in-print version of a paper published online in Science Express on 12 February 2004. That report,“Evidence of a Pluripotent Human Embryonic Stem Cell Line Derived from a Cloned Blastocyst,” was a collaboration led by Woo Suk Hwang and a team of more than a dozen collaborators. The work was done at Seoul National University in South Korea. When the results were announced at a press briefing at the AAAS Annual Meeting in Seattle, well over a hundred reporters and over 20 television cameras were on hand, and the subsequent coverage in the media has been intense.

This is an opportune moment for review: The 3-week interval has provided a good gestation time for reactions. These reactions, some hasty and others thoughtful, form an interesting study of how new scientific findings may become incorporated into a policy framework that is developing under intense political pressure. To begin with the science itself, what the researchers did is to inject enucleated ova, derived from financially uncompensated women who volunteered, with somatic cell nuclei taken from the same donor. Blastocysts were produced by this procedure, and from one of them a stem cell line was produced and propagated through 70 divisions. The pluripotency of these cells was established in ways that left little doubt that they were true embryonic stem cells, although the investigators concede that their experiments have not quite eliminated the possibility of a parthenogenetic origin.