A series of [(o-acylaryl)oxy]propanolamines have been prepared and evaluated for multidrug resistance-reverting activity in a human tumor cell model. Structure-activity relationship studies indicate that the phenylpropiophenone moiety as well as the substitution pattern at the nitrogen atom is crucial for activity of the compounds. Incorporation of the ether oxygen into a benzofuran substructure, which renders the compound an arylethanolamine, decreased biologic activity. Highest activity could be observed with the arylpiparazines 4f-h, which not only completely restored daunomycin sensitivity but also showed moderate activity in restoring etoposide toxicity.