Polyene compounds represented by the general formulae ##STR1## in which: R and R.sub.1 are each hydrogen or an alkyl group of from 1 to 5 carbon atoms;R.sub.2 is an alkyl group of from 1 to 5 carbon atoms;R.sub.3 is hydroxyl, alkoxy of from 1 to 5 carbon atoms, NH.sub.2, NHR.sub.2 or NR.sub.2 R.sub.2 and Z is a cycloalkyl, cycloalkenyl or cycloalkdienyl group substituted with from 0 to 5 alkyl groups, a keto group or a hydroxyl group or a phenyl group substituted with from 0 to 4 hydroxy, alkoxy, alkyl, aryloxy, aralkyloxy or trifluoromethyl groups or halogen atoms or combinations thereof and the pharmaceutically-acceptable salts thereof.The foregoing compounds have been found to be effective in the treatment of psoriasis, inflammatory conditions and allergic responses.