The 2R*,11bS* and 2S*,11bS* diastereoisomers of the spiro[1,3,4,6,7,11b-hexahydro-2H-benzo[a]quinolizine-2, 5'-oxazolidin-2'-one] system were prepared by stereoselective methods. Evaluation of these compounds for antihypertensive activity by oral administration to the spontaneously hypertensive rat showed the 2S*,11bS* series was the more potent. Within that series it was found that small alkyl substituents at positions 3 and 4' enhanced antihypertensive activity and that methoxyl substitution at positions 9 and 10 was optimal. (2S,3S,11bS)-Spiro-[2-ethyl-9,10-dimethoxy-1,3,4,6,7, 11b-hexahydro-2H-benzo[a]quinolizine-2,5'-oxazolidin-2'-one] [(-)-9e] was one of the most efficacious compounds of this series, while its antipode, (+)-9e, was inactive. Selected compounds in this series were shown to be alpha-adrenoceptor antagonists.