Working definitions What is measured in experimental studies and the results of such measurements are often generically referred to as ‘endpoints’. Other terms are also used, e.g. ‘outcome’, ‘response’, etc. In order to make some clarity, working definitions are proposed here. These definitions should be interpreted as specific for this protocol. Similar, but slightly different definitions of the same terminology are reported elsewhere (e.g. U.S. EPA, 2003). This is not an attempt to overrule such existing definitions, but rather to make operative concepts that are relevant for the present project, and to ensure consistency between the assessment of human health and the environment. Assessment endpoint: a parameter which is monitored and/or measured in one experiment. This may have a continuous, discrete, or dichotomic nature. Different assessment endpoints may be grouped in families of assessment endpoints when they refer to a common process (e.g. reproduction, development, DNA damage, apoptosis, oxidative stress, etc.) Measured endpoint: the results of the measurements of the assessment endpoint. Depending on the nature of the endpoint, this may be expressed with a classification (e.g. positive/negative; present/absent) or with a quantification of an effect level by using a certain metric, often in comparison to a negative control. In some cases, the measured endpoint expresses the link between the effect level and the level of exposure triggering such effect.