Addition of the anion from 3-(p-methylbenzenesu1finyl)prop-1-ene to substituted benzaldehydes affords mixtures of α- and γ-products. The diastereoisomeric ratios. which were determined by 1H n.m.r. spectroscopy, appeared relatively independent of electronic factors. Possible transition state models to account for the stereochemical aspects of the reaction are discussed.