Environmental planning takes advantage of geographic information systems (GIS) to manage geographic data. GIS are, however, tools which require a great deal of training and programming expertise and, furthermore, have little support for decision makers during their planning activities. This paper presents WOrkflOw-based spatial Decision Support System (WOODSS) - a software developed at the University of Campinas, Brazil, to be used in conjunction with a GIS in order to provide spatial decision support involving environmental data. WOODSS was implemented on top of a commercial GIS and tested in the context of agri-environmental planning activities. WOODSS is centered on dynamically capturing user interactions with a GIS in real time and documenting them by means of scientific workflows. It keeps track of decision procedures, models applied and the choice of parameters in running these models, WOODSS's workflows can be updated on the fly, allowing testing and comparison of alternative planning strategies. They can, furthermore, be used as building blocks for the construction of complex decision procedures, supporting a divide-and-conquer problem solution style. These workflows interact directly with the GIS, sparing environmental planners and decision makers the burden of low-level programming. (C) 1999 Elsevier Science B.V. All rights reserved.2741671105123