US stem-cell researchers had reason to celebrate last week. The uncertain fate of human embryonic stem-cell lines from the George W. Bush era became a bit clearer as the National Institutes of Health (NIH) moved to approve one of the lines most widely used during the past decade.

Last July, after President Barack Obama overturned his predecessor's restrictive stem-cell policy, the NIH announced new rules on using human embryonic stem cells in federally funded research. Since then, the number of available lines on the government's stem-cell registry has already reached 42 — double that of Bush's day — but none of the 21 lines approved under Bush has yet received the go-ahead under the new rules.

To become eligible for funding, cell lines have to be reviewed on a case-by-case basis to ensure that they were derived from excess embryos used for in vitro fertilization and were donated voluntarily, without inducement. Notably, researchers hoping to apply for grants using two Bush-era lines from the WiCell Research Institute in Madison, Wisconsin — H1 and H9, which account for some 70% of stem-cell shipments from the National Stem Cell Bank — had been left in limbo for the past six months.

"Once we learned about not being able to use the cell lines, there was a lot of uncertainty about what to do," says Thomas Zwaka, a biologist at Baylor College of Medicine in Houston, Texas.

On 22 January, the advisory committee to NIH director Francis Collins told him to give H1 the thumbs up, but said the line's usage should be restricted according to the consent forms signed by the embryo donors in 1998. The NIH generally allows stem cells to be combined with the cells of non-primate animals, but donors of the H1 cells signed a form that indicated that cells would not be mixed with those of any other embryo, human or animal. Collins says the general policy for all lines will be to post the exact language of consent forms on the stem-cell registry.

Janet Kelly, a spokeswoman for WiCell, says the institute plans to submit an application for H9, along with three other lines, as soon as possible.