Beliefs about the environmental harmfulness of consumer goods are often considered as a crucial determinant of green purchasing behaviour. Accordingly, ecolabels are expected to provide consumers with the necessary information in order to distinguish between environmentally friendly products and more harmful products. However, no research so far examined the mechanism through which perceived harmfulness influences decision making. Based on a quasi-experimental design, this study tests the effect of environmental labelling on participants' choice between a store brand and a national brand, in two different product categories. Our findings confirm that differences in perceived harmfulness have a significant impact on choice. This link is moderated by product category, environmental concern and price sensitivity