It was eight years in coming — which felt like eons to some researchers — but on March 9, President Obama rescinded his predecessor's Executive Order prohibiting the use of federal money to fund research on stem cells. A congressional law still prevents scientists from using government funds to create new lines of embryonic stem cells, which can develop into any of the body's tissues, but at least scientists are now free to use that money to study the hundreds of stem-cell lines already in existence. Before embarking on such research, however, scientists had to wait for a working group at the National Institutes of Health to vet the stem-cell lines and ensure that they were generated responsibly, according to stringent ethical and scientific principles. In December, the first lines to pass this test became available.