New tetrahydropyrimido[4,5- b]quinolines, hexahydropyrimido[4,5- b]quinolines, a thioxohexahydropyrimido[4,5- b] quinoline, an octahydropyrimido[4,5- b]quinoline and a tetrahydro[1,2,3]triazino[4,5- b]quinoline have been synthesised. A series of S-alkyltetrahydroprimido[4,5 -b]quinolines was obtained by the reaction of the thioxohexahydropy-rimido[4,5 -b]quinoline with allyl bromide, propargyl bromide or with epichlorohydrin. All newly synthesised compounds were characterised by IR, 1H, 13C NMR and elemental analysis.