The possibilities and limitations of applying the eddy break-up model to non-premixed flames is analyzed. The purpose is to explain the apparent success of the model and to point out problems that are encountered when combining the model with a multistep reaction mechanism. The model can be used in the anal. of hydrocarbon flames with 4-step mechanism. The shortcomings of the model are discussed. Effect of temp. fluctuations on the reaction rate, the eddy break-up model and finite rate chem., and methane-oxygen flame calcns. are considered.