Using the Wood-Bonhoeffer method, an investigation has been made of the reaction of deuterium atoms with methane at temperatures up to 500 °C. Owing to the difficulties involved in poisoning the walls to prevent atom recombination at high temperatures, the atom concentration was very variable. The results are therefore only approximate, but they serve to establish definitely the presence of a reaction at the temperatures under investigation, and enable the estimation of the activation energy of the reaction[Formula: see text]viz., 12.9 ± 2 Kcal. This is in good agreement with values obtained in other investigations.