A mild method for 1,2-addition of alkyl disulfides to alkenes and conjugated polyenes catalysed by MClx-promoted montmorillonite clays is reported. Alkenes undergo 1,2-trans addition affording MClx-complexed derivatives, which are readily converted to alkylthio-derivatives on reaction with EDTA. Conjugated polyenes yield 1,2-trans addition and 1,n-addition products, with 1,2-addition compounds being found at low reaction temperatures.