It is well-known that unit-based pricing systems have a significant effect on the quantity of collected waste. Part of this effect may, however, result from a selection bias or environmental activism effect. Based on a pooled cross-section for the Netherlands for 1998-2005 we show that despite the correction for environmental activism the effect of the weight and bag unit-based pricing system on the quantity of waste is sizeable. Moreover, this environmental activism effect is decreasing over time, so that the most environmental friendly municipalities implement unit-based pricing systems at first. In addition, we show that the volume effects of the different unit-based pricing systems are rather stable over time. Although we find some evidence for a learning effect, nearly no evidence is found for an awareness erosion effect. This means at least that the effect of unit-based pricing does not decrease over time, which is reassuring from an environmental point of view. Pricing waste helps. © 2008 Elsevier B.V. All rights reserved.