In this article we address the question of how, given information about the reaction fluxes of a system, flux values can be assigned to the elementary modes of that system. Having described a method by which this may be accomplished, we first illustrate its application to a hypothetical, in silico system, and then apply it to fermentation data from Lactobacillus rhamnosus. This reveals substantial changes in the flux values assigned to elementary modes, and thus to the internal metabolism, as the fermentation progresses. This is information that could not, to our knowledge, be obtained by existing methods. The relationship between our technique and the well-known method of Metabolic Flux Analysis is also discussed. (C) 2004 Wiley Periodicals, Inc.