This paper outlines recent developments in the provision of Geographical Information Systems (GIS) and associated spatial decision support systems (SDSS) over the WWW. The potential of giving open access to data and decision support tools relevant to a particular environmental problem are discussed in the context of improving public involvement in the decision-making process. Work currently in progress at the University of Leeds on a web site covering the problem of where to site a new radioactive waste disposal facility in Britain is described in detail. The aims of this work are to: (a) investigate the potential of WWW-based SDSS for addressing public participation and consultation issues in important environmental decisions; (b) provide the public with access to appropriate spatial databases and analysis tools to enable informed personal decisions to be made about a difficult geographical problem; and (c) gain some insights into how users perceive geographical decision problems and in what way the characteristics of the individual may influence the decisions made. The web pages providing background information to the radioactive waste disposal problem are described in brief before discussing the GIS-SDSS architecture of the web pages in more detail. Preliminary results and feedback from live tests are presented. Conclusions focus on plans for future research together with a brief discussion of the practical and ethical problems surrounding the use of the WWW as a medium for wider public involvement in environmental decisions.