It is a widely accepted claim that scientific practice contains value judgments, i.e. decisions made on the basis of values. This paper clarifies the concepts involved in this claim and explains its implications for risk assessment. It is explained why values are necessarily a part of science and of risk assessment. A certain type of values that contribute to the aim of science, so-called epistemic values, are identified as rationally justified as basis for judgment in science. It is argued that the aims of pure science and risk assessment differ in some aspects and that consequently pure science's epistemic values are not sufficient for risk assessment. I suggest how the epistemic values may be supplemented in order to align better with the aim of risk assessment. It is concluded that since risk assessment is no less value-laden than pure science, it is important (a) that risk assessors become aware of what values they are (often implicitly) relying on, (b) that the values are justifiable, and (c) that transparency is ensured, i.e. that the values and value-based assumptions applied in particular risk assessments are explicitly acknowledged. (C) 2004 Elsevier Ireland Ltd. All rights reserved.