A materials balance is an array of the flows of materials or chemicals from the cultural environment to the first point of entry into the natural environment and includes information regarding the location, time rate, quantity and chemistry of the flows. The materials balance encompasses two major components--identification of sources and materials and estimates of environmental loadings. The scope and focus of a materials balance is determined by various characteristics, such as geographic scale, time frame, environmental media or chemical class. Feasibility criteria are presented to evaluate the various approaches. The feasibility criteria are degree of uncertainty in source or quantities, human resource requirements, time constraints, identification of controllable sources, applicability to exposure predictions, comprehensiveness of the method, ability to use similar chemicals as guides, interfacing with fate models, accuracy of results, compatibility with existing data, applicability of method to different geographic scales, resolution of results in time and space, requirements for monitoring data, use of confidential information, data processing demands and complexity of input data and method.