This article contains the results of a study performed to support the Dutch environmental policy of dematerialization. The aim of the study was to develop and apply a methodology to identify the materials that contribute most to the environmental problems in the Netherlands. The developed methodology combines aspects of material flow accounting (MFA) and life-cycle assessment (LCA) and aims at adding a set of environmental weights to the flows of the materials. The methodology was applied to a number of materials. For these materials, impacts per kilogram were extracted from a standard LCA database in combination with standard LCA software. These impacts per kilogram are then multiplied with the yearly throughput of each material in the Netherlands to obtain an indication of the environmental impacts associated with each material. This article contains a discussion of dematerialization as background for the research, a description of the methodology followed by the results of its application, and a discussion of the comparison of impact-based versus mass-based indicators. Materials vary many orders of magnitude in their impacts per unit mass. In general, the impact per unit of mass of bulk materials is lower than that of materials used in small quantities. This implies that the variation in orders of magnitude of impact multiplied by mass is much less than either mass or impact per kilogram separately. High-priority materials based on impact multiplied by mass are either small-quantity materials with very high impacts per kilogram (such as heavy metals) or large-quantity materials with not-so-low impacts per kilogram (such as materials from agriculture and plastics).