Reaction of dialkyldisulfides or diselenides with allenes is catalyzed by a rhodium-phosphine complex and trifluoromethanesulfonic acid giving (E)-2-alkylthio(seleno)-1,3-dienes and (E)-2-alkylthio(seleno)-2-alkenes. Unlike the reaction of alkynes, the reaction of allene is accompanied by hydridetransfer.