Which app? If Safari, AFAICT, there is no text under the toolbar buttons. If Finder, then if you've selected Show Icon & Text, deselect Use small size. Details will help.
I thought they in Safari, BUT I just checked them out, and they are actually the text in the Bookmarks Bar (not connected to icons). Sorry I wasn't clear.
Thanks for clarifying. Two options, use a lower resolution or System Preferences->Universal Access and turn Zoom on (also, click on options and select Use scroll wheel with modifier keys if you have a mighty or magic mouse).