A striking difference in antimalarial activity between the diastereomers of 6-bromo-alpha-[2-(1-methylpiperidyl)]-9-phenanthrenemethanol, alpha-(3-peperidyl)-3,6-bis(trifluoromethyl)-9-phenanthrenemethanol, and alpha-(3-piperidyl)-2,8-bis(trifluoromethyl)-4-quinolinemethanol was observed. A possible explanation involving the N-O distance and active site binding requirements is suggested.