The Animal Welfare Act (AWA) regulations require principal investigators to consider alternatives to procedures that may cause more than momentary or slight pain or distress to the animals and provide a written narrative of the methods used and sources consulted to determine the availability of alternatives, including refinements, reductions, and replacements.
USDA APHIS Animal Care Policy Manual
Policy 12: Consideration of Alternatives to Painful/Distressful Procedures
Search for Alternatives (Altweb)
AltWeb is a clearinghouse for information on alternatives to animal testing.