Livestock that result from biotechnology have been a part of agricultural science for over 30 years but have not entered the market place as food or fiber.  Two biotechnologies are at the forefront as challenges to the world's systems for regulating the market place: animal clones and transgenic animals.  Both technologies have come before the Food and Drug Administration in the United States and it appears that action is imminent for clones.  The FDA has asserted principles for evaluation of clones and asserts that '? remaining hazard(s) from cloning are likely to be subtle in nature.' The science-based principles recognize that in some areas related to developmental biology and gene expression in clones, additional scientific information would be useful.  The role of science then is to use the genomic tools that we have available to answer questions about epigenetic regulation of development and reprogramming of genes to the state found in germ cells.  Transgenics pose additional challenges to regulators.  If the transgenics are produced using cloning from modified cells then the additional scientific information needed will be related to the effects of insertion and expression of the transgenes.  Other approaches such as retrovirally vectored transgenesis will elicit additional questions.  These questions will be challenging because the science will have to be related to the expression and function of each gene or class of genes.  For the promises of animal biotechnology to be fulfilled, scientists will have to resolve many questions for regulators and the public but tools to answer those questions are rapidly becoming available.