Since 1998, the volume of research being conducted using human embryonic stem (h ES) cells has expanded primarily using private funds because of restrictions on the use of federal funds for such research. Given limited federal involvement, privately funded h ES cell research has thus far been carried out under a patchwork of existing regulations, many of which were not designed with this research specifically in mind. In addition, h ES cell research touches on many ethical, legal, scientific, and policy issues that are of concern to the public. This report provides guidelines for the conduct of h ES cell research to address both ethical and scientific concerns. The guidelines are intended to enhance the integrity of privately funded h ES cell research by encouraging responsible practices in the conduct of that research.