The NIH-HSCF has routinely grown hES cells on the NIH registry from August 2003. In the following year, most of the hES cells on the NIH registry were obtained, expanded in culture and analyzed by karyotype and FACS analysis. In the period to 8/2004, the central achievement of NIH-HSCF was to show that sub-clones of a hES cell line had a stable genome using a high-resolution genome scanning method. This evidence that hES cells can be grown for long periods without genetic change suggested that they might provide an important resource in the urgent quest to better understand and treat human disease. The next major focus was to grow the cell lines following a standard procedure. When they were first established, laboratories around the world used different procedures to obtain relatively few stable cell lines. This stage of the work was carried out in an international collaboration organized through the International Stem Cell Consortium. The ISCC is sponsored by the International Stem Cell Forum, a grouping of research agencies in several countries including Australia, Canada, Israel, Sweden, the United Kingdom and the United States. The ISCC defined a set of antibodies and a gene array as standard tools to assess hES cells. The ISCC also promoted standards to determine the safety of hES cell lines. At this stage, the NIH-HSCF was one of the few sites contributing multiple hES cells from different providers grown under standard conditions. The outcome of these studies was increased confidence that hES cells could be maintained in a similar state in laboratories around the world. It is important to point out that human ES cells are difficult to grow because they are poised to differentiate into all the cell types of the body. Based on other work in LMB/NINDS that defined the cellular and molecular basis for the self-renewal/differentiation switch, the NIH-SCF optimized growth conditions for undifferentiated hES cells. This information and gene expression data on different hES cell lines is accessible on the NIH Stem Cell Facility web site. Current work in the NIH-SCF is aimed at providing assurance that this efficient growth method applies to all human ES cells and induced pluripotent stem (iPS) cells. The strong similarity between human ES cells and iPS cells defined by high-resolution tools suggests the analysis of human pluripotent cells will be rapidly implemented in human genetics laboratories. In this effort, the data bases, cell banks and procedures developed in the NIH-SCF are a core resource for researchers at NIH and the wider community of researchers defining the genetic basis of human disease.