List boxes are a common user interface component in graphical user interfaces. In practice, most list boxes use right-oriented scroll bars to control left-justified text items. A two-way interaction hypothesis favoring the use of a scroll bar orientation consistent with list box item justification was examined for speed of use and user preference in two experiments. A two-way interaction was obtained in both experiments. Item selection was faster with a scroll bar orientation consistent with list item justification. Subjects preferred right-oriented scroll bars with right-oriented text items. There was no difference in preference between right and left-oriented scroll bars for left-justified text items. These results support a design principle of locality for user interface controls and controlled objects.