Three-dimensional imaging of minor combustion species is of great interest for combustion engineering, process control and environmental analysis. On the other hand, difference frequency generation (DFG) based continuous wave (cw) laser sources offer a compact and low-cost alternative light source for high resolution spectroscopy. In this work, difference frequency generation (DFG) laser light sources are used in the mid infrared (MIR) for the optical tomography of combustion products, such as carbon monoxide, in laminar CH4/air flames on a flat flame burner. The combination of DFG MIR spectroscopy and computerized tomography is shown to offer great potential for laminar flames, as well as environmental monitoring. (C) 2004 The Combustion Institute. Published by Elsevier Inc. All rights reserved.