Human embryonic stem cell (hESC) research has sparked incredible scientific and public excitement, as well as significant controversy. hESCs are pluripotent, which means, in theory, that they can be differentiated into any type of cell found in the human body. Thus, they evoke great enthusiasm about potential clinical applications. They are controversial because the method used to derive hESC lines destroys a 2- to 4-day-old human embryo. Research and discoveries using human pluripotent stem cells (hPSCs) are simultaneously cutting-edge contributions to fundamental understanding and potentially invaluable sources of new treatments for some of our most devastating diseases and injuries. However, federal funding restrictions, legal challenges, and public controversy continually impose on the field's development. Thus, hESC research also offers a laboratory for examining the effects high-level science policy decisions have on the trajectory of an emerging scientific field. Today, nearly 15 years after the discoveries that made hPSC science feasible, continued federal funding for this research is highly uncertain.These authors believe that federal funding for hPSC science should be expanded and stabilized through legislation. By this, they mean three related things: (1) the volume of funding for hPSC research should be increased; (2) the range of cell lines and methods of derivation eligible for funding should be encouraged to grow; and (3) federal funding for hPSC research should be regularized through unambiguous legislation allowing researchers to plan and execute their often technically challenging, uncertain research programs on stable institutional ground. The authors' position is based on three observations: (1) They note that both the clinical and the scientific potentials of hPSC research are beginning to be realized. Expanded regularized research support will accelerate those trends; (2) Widely-accepted ethical standards and effectively implemented institutional rules make the expansion of federal support for hPSC research unproblematic; and (3) The uncertainty, ongoing controversy, challenges, and rule revisions imposed on stem cell scientists may be as damaging to the field as are restrictions. (Contains 6 footnotes.)