A non-intrusive technique for measuring the concentration of gaseous species in reacting and non-reacting sprays is presented. Infrared absorption is the basis for the measurement. In a two-phase situation. the light scattered by particles can be deduced by measuring extinction of wavelengths at which no absorption occurs. As a result. combined infrared extinction and scattering (IRES) is employed for two-phase flows. The technique. although based on line-of-sight absorption. has the potential to be spatially-resolved for either symmetric or asymmetric fields depending upon the deconvolution technique applied. The technique is demonstrated using a single phase methanol vapor/air free jet and non-reacting and reacting methanol sprays. To complement these results. measurements of droplet size and velocity as well as gas velocity can be achieved using other non-intrusive approaches such as phase Doppler interferometry. These complementary measurements may be combined with the concentration measurements to quantify vaporization. The results illustrate the applicability of this relatively inexpensive and simple technique which adds valuable information to the study of sprays.