An assumed probability density function (PDF) approach that accounts for temperature and composition fluctuations, including effects of temperature-composition correlations, has been developed. Parametric studies were performed to determine the gross behavior of the assumed PDF and provide insight into the expected trends of the model for a given kinetic mechanism. The model was implemented into an existing Navier-Stokes solver and applied to a supersonic, co-axial H-2/air burner. Proper prediction of the turbulence effects on the chain initiating step of the kinetic process is a first-order concern in supersonic combustion applications because of small flow residence times. Temperature-composition correlations were extracted and compared with results obtained by direct integration of a PDF evolution equation. The results of this comparison showed that the model properly predicted both the magnitude and sign of the cross-correlation terms associated with the chain initiating step of the H-2/air kinetic mechanism. Correlations for all but one of the remaining kinetic steps qualitatively reproduced those obtained by direct integration. (C) 2003 The Combustion Institute. All rights reserved.