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Instantaneous values of temperature and major component concentrations have been measured simultaneously using pulsed Raman spectroscopy in hydrogen-air diffusion flames of low turbulence produced in a well-controlled co-flowing fan-induced combustion tunnel. Results are presented in the form of probability density functions for each of these scalar variables as a function of flame position. Simultaneously measured values of temperature and concentration (nitrogen or hydrogen) are compared with adiabatic equilibrium flame calculations of these variables. Close agreement with this simplified escription is obtained in the lean regions of the flame; in the fuel-rich regions, the concentrations of N2are higher than theoretically predicted and those of H2are lower. Analysis strongly suggests that these systematic deviations arise from differential diffusion of H2. Initial conditioned sampling measurements are reported for hydrogen-propane-air turbulent diffusion flames and for premixed laminar propane-air flames.