Technical Abstract: Attraction to the contents of old nests was examined in the blue orchard bee, Osmia lignaria and the alfalfa leafcutting bee, Megachile rotundata. Mated, inexperienced females of the same age were subjected to Y-tube tests in which they could move towards an airstream flowing through an empty blank or through a capsule containing material that may be found in old nesting material. For O. lignaria, the materials tested against the blank were empty female cocoon, paper straw used as nesting cavity, female meconium, feces, and mud plug. For M. rotundata, the materials tested against the blank were empty female cocoon, leaf pieces used in cell construction, female meconium, and feces. Each nesting material was also tested against all the other materials for M. rotundata. Nest materials were examined using gas chromatography/mass spectrometry in order to find chemical components that may be the attractive to these cavity-nesting bees. This study may help in the development of more attractive, clean nesting material, a desirable commodity in the management of these economically important solitary bees.