Balance equations for mass, velocity, and Reynolds stresses conditioned either to an unburned or to a burned mixture are derived from standard mass conservation, Navier-Stokes, and combustion progress variable balance equations by assuming that the probability of finding intermediate states of a reacting mixture is much less than unity. The derived equations contain three unclosed terms controlled by flamelet structure and flamelet statistics, whereas other unclosed terms are not straightforwardly affected by heat release and have counterparts in models of nonreacting flows. Equations of this type offer an opportunity to facilitate modeling the effects of heat release on turbulence. The modeling of these effects is further simplified if flamelet structure perturbations by turbulent eddies are neglected. (c) 2007 The Combustion Institute. Published by Elsevier Inc. All rights reserved.