A process for the production of bis-[O-(1-alkylthioethylimino)-N-methylcarbamyl]-N,N-sulfides of the formula I ##STR1## wherein R is a straight-chain or branched alkyl group of 1 to 5 carbon atoms, by reacting a O-(1-alkylthioethylimino)-N-methylcarbamate of the formula ##STR2## wherein R is as defined above, in the presence of a base, with sulfur dichloride or sulfur monochloride in an inert solvent, which process comprises carrying out said reaction in the presence of 0.01 to 0.5 mole of a compound selected from the group consisting of N,N-dialkylformamides, each containing 1 to 4 carbon atoms in the alkyl moieties, N-methylpyrrolidone, dimethyl sulfoxide, phosphoric acid tris-N,N-dimethylamide and tetramethyl urea, per mole of O-(1-alkylthioethylimino)-N-methylcarbamate of the formula II.The bis-[O-(1-alkylthioethylimino)-N-methylcarbamyl]-N,N'-sulfides of the above formula possess insecticidal properties and are suitable in particular for controlling pests of cotton plants and bluebottles.