The thiomethylation of propanol, butanol, cyclohexanone and acetophenone with a mixture of formaldehyde and sodium sulphide proceeds at 20 degrees C and normal pressure for 1-7 hr. It has been established that the reactivity of ketones increases in the order butanone-cyclohexanone-propanone-acetophenone. The conversion of sodium sulphide depends on its initial concentration, the nature of the ketone, and the presence in the reaction medium of sodium hydroxide and ethyl alcohol. It has been shown that the reaction proceeds with the preferential formation of keto-and diketosulphides.