Optically active poly(gamma-ketosulfide)s having the asymmetric centres in the main chain have been prepared by polyaddition of 1,3-dimercaptobenzene to trans,trans-dibenzylidene acetone in the presence of catalytic amounts of chiral amines. The extent of asymmetric induction on the polymeric product is found to be dependent on the type of amine, cinchona and ephedra alkaloids giving the highest optical activity in the polymer, due to the presence of the beta-hydroxy amine moiety, which favours the formation of tight transition states involving both the reactants. The corresponding low molecular weight analogues have also been synthesized. The stereochemical features have been investigated by n.m.r. and the chiroptical properties studied by circular dichroism measurements. The results indicate that comparable asymmetric induction is found in polymers and model compounds, the former systems not exhibiting appreciable evidence of ordered secondary structures, in agreement with a low degree of stereoregularity along the macromolecular backbone.