Sir

The Hwang case highlights issues in human egg donation that were not addressed in your Editorial “Standards for papers on cloning” (Nature 439, 243; 2006). Developing clones with eggs obtained from one's employees raises serious ethical concerns (see D. Magnus and M. K. Cho Science 308, 1747–1748; 2005).

First, there is considerable risk that the decision to donate is made under pressure and is not entirely voluntary. Second, donors may not be adequately informed. For example, if donated eggs are sought purely for research purposes, the donor must know that they will not be used to develop therapies. Scientists, like all professionals, have an ethical imperative to serve certain socially valued goals, but they must not violate others' autonomy in the pursuit of those goals.

Human eggs are not easily obtained: the process involves trips to a clinic, ultrasound scans, injections to stimulate egg production and, when appropriate, having a probe with an attached needle guided by ultrasound inserted through the vaginal wall into the ovary to remove the eggs. Researchers using human eggs should be independent of any fertility clinics treating the women from whom the eggs came. That way, women are less likely to feel coerced into donating their eggs, and it helps ensure that clinical decisions are not motivated by either scientific or financial gain in the pursuit of these unique stem-cell lines. Cloning publications should include clear information about the steps taken to ensure that egg donors gave their informed and voluntary consent to donation.