The Food and Drug Administration (FDA) is publishing a guidance entitled "S4A Duration of Chronic Toxicity Testing in Animals (Rodent and Nonrodent Toxicity Testing)." The guidance was prepared under the auspices of the International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) and is intended to provide guidance on the duration of chronic toxicity testing in rodents and nonrodents as part of the safety evaluation of a drug product. FDA is also noting circumstances in which it may accept durations of chronic toxicity testing in nonrodents that differ from the duration generally recommended by ICH.