A small-scale method was first developed in which the degree of chlorination of methane to methyl chloride could be determined by analysis of the resulting gases. The optimum conditions so determined were then applied on a scale which permitted the isolation and measurement of the products. A yield of 80% or better was obtained when using as a catalyst partially-reduced cupric chloride and passing moist nitrogen, methane and chlorine in the ratios of 70:7:1 at 450 °C. It was found that the proportion of chlorine could be more than doubled when 8% of hydrogen was present in the methane. Under such conditions the chlorine was completely utilized and only methyl chloride and hydrogen chloride were formed. The yield of isolated methyl chloride obtained was nearly 80% and this could be increased by operating on a larger scale. The same catalyst was successfully used in the chlorination of methane to carbon tetrachloride. A yield of 90% was obtained, with complete utilization of the chlorine. The chlorination of ethane to ethyl chloride, with a yield of at least 75% was also shown to be possible.