We discuss the use of fixed wavelength infrared absorption measurements as a means for observing compositional changes in MOVPE process gas mixtures using relatively simple instrumentation consisting of an incandescent lamp, a narrow bandpass filter matched to the CH stretch modes of the alkyl precursors, and an infrared detector. An advantage of this setup is that the low energy of the infrared radiation does not induce photolysis reactions on the analyser cell windows in contrast to ultraviolet-based techniques. We present preliminary data on gas composition measurements obtained in the alkyl lines of an MOVPE reactor and show that useful information can readily be obtained on absolute gas concentrations, gas switching transients, and reactor line memory effects.