3R principle
Russell, William M.S. / Burch, Rex L. (1959): The Principles of Humane Experimental Technique. London: Methuen, especially pp. 69-154. Online Version
German Federal Institute for Risk Assessment (BfR) Online Version
European Union Reference Laboratory for alternatives to animal testing (EURL-ECVAM) Online Version
European Partnership for Alternative Approaches to Animal Testing (EPAA) Online Version