The laminar flamelet model in combination with joint probability density function transport equation of mixture fraction and turbulence frequency is used to simulate turbulent jet diffusion flames of hydrogen. The frequency distributions of radiative source terms are calculated for four important infrared bands of water vapor. The results show that, for the given ensemble, about 95% samples of radiative source term for each band locate within the region of +/-3.0 standard deviation of the mean radiative source term. Due to the different relation between band intensity parameters and temperature for every band, the symmetrization of frequency distributions for each band is different. (C) 2004 Elsevier Ltd. All rights reserved.