Novel enantiomeric and diastereoisomeric forms of decahydroquinolines of the formula ##STR1## wherein R.sub.1 and R.sub.2 are individually selected from the group consisting of hydrogen and alkyl of 1 to 5 carbon atoms or taken together with the nitrogen atom to which they are connected form a 5 to 6 member heterocycle optionally including another heteroatom and optionally substituted, A is selected from the group consisting of --(CH.sub.2).sub.n -- and alkylene substituted with an alkyl and having 2 to 8 carbon atoms, n is an integer from 0 to 5, Z is selected from the group consisting of optionally substituted phenyl, naphthyl indenyl, monocyclic heterocycle of 5 to 6 members and a bicyclic heterocycle all being unsubstituted or substituted by one or more substituents and their non-toxic, pharmaceuically acceptable acid addition salts and quaternary ammonium salts having central analgesic properties.