Technical Abstract: The Megachilid bees Osmia lignaria Say, Megachile rotundata (F.) and M. pugnata Say were tested for attraction to various components associated with their nesting cavities, or chemical extracts of these components, using a Y-tube olfactory response bioassay. As these bees preferentially nest near old nest cavities, nest components may be important in providing cues to females looking for nesting sites. Results show that the females are attracted to components which might harbor species-specific cues or that may indicate nesting activity.