Scientists at a laboratory affiliated with the University of Wisconsin-Madison have developed a stem-cell culture medium free of animal cells and used it to derive two new human embryonic stem-cell lines. The new work, reported in the journal Nature Biotechnology, is a crucial step in stem-cell research because it will allow growth of these cells without using animal products that can harbour viruses and other potential sources of problems. "This work helps us clear some of the major hurdles for using these cells therapeutically,' wrote Tenneille Ludwig, the UW-Madison research scientist at the Wi-Cell Research Institute, who led work.