Single-point closure models for single-step chemical reactions in decaying homogeneous turbulence-and some associated experiments and simulations-are briefly reviewed. Three of these models for the reaction term in the concentration field equations are evaluated by comparison with direct numerical simulations. In agreement with other studies of non-premixed single-step reactions, the reactant concentration variance shows little sensitivity to Damkohler number, although the segregation coefficient depends strongly on it. Toor’s model, which hypothesizes that the reactant concentration covariance is independent of the Damkohler number, agrees with simulation data better than do the models of Patterson and of Dutta and Tarbell; however, an attempt to remove a shortcoming of Toor’s hypothesis by using an initially Gaussian conserved scalar did not improve its behavior.