Direct numerical simulations were used to study chemical selectivity in a series-parallel reaction scheme in a decaying, homogenous turbulent flow, where A, B, R, and S represent chemical species with R the principal product and S the secondary product. These simulations involve solution of the unsteady Navier-Stokes and mass conservation equations by a pseudo-spectral method in a 64(3) wavenumber domain. Reactants A and B were initially spatially segregated, corresponding to a nonpremixed system. The effect of turbulence Reynolds number and other physical parameters on selectivity was determined Turbulence increases the formation of primary product R over byproduct S compared to the case of no fluid motion, as expected. It was also found that any mechanism promoting homogenization of reactants favors the formation of R, whereas any mechanism sustaining segregation favors the formation of S.