Previous publications on the title compounds, 1 and 2 ('A-4' and 'A-5'), reported pharmacological data on what were probably mixtures of optical isomers of unknown composition. The compounds can exist as an enantiomeric pair as well as a diastereomeric meso isomer. In the present work, all possible stereoisomers (meso and dextrorotatory and levorotatory isomers) of the piperidine derivatives 'A-4' and 'A-5' have been isolated, identified, and characterized, and pharmacological data have been obtained on all products. In all of the bioassays conducted, optical isomers of each structure exhibited similar qualitative and quantitative effects. We conclude that the stereochemical nature of the chiral centers bearing secondary alcohol groups in these molecules does not play a critical role in interactions with in vivo receptors, and therefore that the alcohol groups in 'A-4' and 'A-5' are not prime sites of interaction(s) with receptor(s).