As the number of new chemicals used in industry, food and consumer products is constantly increasing, so is the chemical release to the environment, and the need to understand the adverse effects of chemical mixtures becomes increasingly urgent. In addition, chemicals may act in combination with non-chemical stressors (e.g., radiation, temperature, pH etc.) to produce unexpected multiple stressor effects. Even though the concentration or dose of each single stressor may be low in the environment, the potential for harmful effects from the mixture of stressors has worried researchers for years. No one has yet been fully able to predict the effects of multiple stressors; but a new concept and approach developed by researchers at the Norwegian Institute for Water Research (NIVA) is probably one step in the right direction.