A model of laminar, soot-laden ethene diffusion flames has been developed and compared with measurements in nonsooting and sooting flames. Concentrations of stable gas-phase species were measured with mass spectrometry; laser-induced fluorescence was used to measure the OH concentrations. A system of elementary reactions was used to describe the gas-phase chemistry. The model incorporated a simple description of the growth of soot which assumed that acetylene was the only growth species. Soot formation was coupled with the flame chemistry via the loss of acetylene and OH on soot and the production of CO during soot oxidation. The model predicted most of the gas-phase species quite well, with the exception of OW. The loadings of soot in the flames were reproduced adequately, although less success was achieved in predicting the transition from nonsooting to sooting conditions. Details concerning the products of soot oxidation by OH were found to be important with regard to the flame chemistry. The inclusion of soot in the flame model had a significant impact on tile predicted structure of the flame as seen in changes to the formation and destruction rates of OH on the fuel side of the flame. The rate of OH reaction with soot in the midregion of the flame was small compared with the rate of reaction of OH with CO. However, the two rates became comparable in the soot burnout zone,