A package for the analysis of ecosystem flow networks. In a single software package NETWRK affords an ecosystem researcher or manager with several new avenues for extracting heretofore unavailable information about the flows of material or energy in the ecosystem. Clues about how an ecosystem may be reacting to a perturbation are often manifested first as changes in the relationships among the constituent taxa. Systematic analyses that quantify these configurational changes are only now beginning to appear as ecological software. NETWRK consolidates four analytical techniques: (1) The study of indirect trophic effects allows the user to infer how a given taxonomic group affects or is affected by other compartments with which it may not be directly connected. (2) The myriad of trophic interactions is simplified into a linear chain of trophic transfers (sensu Lindeman), revealing how efficiently the system is processing the medium in question. (3) The full structure of pathways of recycle is elaborated, possibly depicting domains of control within the system. (4) The overall trophic status of the system is assessed by several indices deriving from thermodynamics and information theory. A before-after comparison of these system indices allows the user to render quantitative judgements about the extent to which the community in question has been impacted. This nine year old program has been tested extensively and is available for use in both MS-DOS and Macintosh environments in either FORTRAN or Pascal. Copies are available from the authors.