The development of alternative methods to animal experimentation is gaining momentum with an increasing amount of in vitro tests gaining regulatory acceptance. Some are used for screening purposes; others are eventually validated and accepted by the international regulatory bodies. The use of alternatives also has a growing tendency in basic research and in education.

Historically, alternative methods, now also called New Approach Methodologies (NAMs), were defined as methods able to reduce the number of animals necessary in a trial, refine toxicology procedures to make them less painful or stressful, or replace animals with nonanimal (in vitro, ex vivo, or in silico) systems.

Today NAMs include not only in vitro, in silico, and in chemico methods, but also a variety of new testing tools and concepts, such as “high-throughput screening” and “high-content methods” (e.g., genomics, proteomics, and metabolomics) and play an essential role in the hazard identification and risk assessment of toxicology profile of compounds, complex mixtures, medical devices, and drugs.