As of August 2005, 22 human embryonic stem cell (hESC) lines listed on the National Institutes of Health (NIH) hESC Registry were being distributed to investigators. At a June 2005 meeting of NIH-supported hESC researchers, we proposed that a set of shared standards should be available in order to characterize the cells unambiguously in multiple laboratories. Here, we elaborate such a plan to identify a set of standard methods and to initiate collaborative efforts to validate the standards. The standard assays we propose should be comprehensive enough to ensure that hESC banks can provide a consistent and reliable product for NIH researchers, and inexpensive enough that individual laboratories can afford to use at least some of the methods routinely in their laboratories. We expect that as data accumulate and standards evolve, a core set of tests will become the norm for routine assessment of hESC cultures and that these tests will lay the groundwork for clinical applications of these cells.