The Humane Society of the United States recognizes that research on stem cells, which are precursors to a number of different cell types, holds considerable potential for yielding treatments and cures for a variety of human health maladies. The growing field of stem cell research also holds promise for reducing the use of animals in various research areas over the long term. For the immediate future, however, stem cell research applications will most often be conducted in nonhuman animals before application occurs in humans, thereby increasing animal use.

The emerging field of stem cell research is largely exploratory, with many unknowns. It must be recognized that there is considerable potential for the animals used to experience pain and distress, which could be severe. Accordingly, The HSUS believes that stem cell research must be undertaken with due regard for the following principles:

• Careful consideration of all ethical concerns.

• Careful scrutiny of the welfare of animals used.

• Clear justification of the research and species used, because of the potential for pain and distress.

• Vigorous minimization of animal pain and distress, including the use of appropriate pain and distress recognition, assessment and alleviation tools.

• Close monitoring of the literature in order to reduce duplication of effort and to ensure minimization of pain and distress.

The HSUS also recognizes that stem cell research often involves the creation of chimeras (organisms composed of two genetically distinct types of cells; this can include the use of human cells), which encompasses additional ethical concerns of a serious nature. This field of research has the potential for even more serious concerns (for both humans and nonhumans) than those that are a reality today. Creation of chimeras contributes to the debasement of animals as humankind manipulates nature by combining cells of an array of organisms. The HSUS has similar concerns with chimera research as with other types of stem cell research, particularly pain and distress, as discussed above. The HSUS is unequivocally opposed to whole organ xenotransplantation, a specific application of chimera research. For more information, see The HSUS's position statement regarding xenotransplantation.