Lack of selectivity towards anesthetic stereoisomers is one of the few criteria available for the identification of an anesthetic target site. Until now this criterion has not been tested for anesthetics that directly interact with sensitive membrane proteins which are considered the targets of anesthetic action. In this communication we show that stereoisomers of 2-butanol and 2,4-pentanediol did not differ in their inhibitory potency for a site located on the Na+/K+/Cl- co-transporter protein. This suggests that an inhibition site on a membrane protein can fulfill the criterion of lack of stereoisomer selectivity.