The purpose of this investigation was to design, build and test a new system for exposing small laboratory animals to respirable cotton dust. Two of the most important considerations of the design were 1) the exposure environment should remain constant with respect to time and 2) only a minimum amount of bulk cotton dust material should be necessary to generate the respirable cotton dust aerosol. By requiring less bulk cotton, it would be possible to conduct more studies with a given amount of dust, and new studies would be possible which were not limited to using a large sample of an 'average' cotton dust. Last year we described how the performance of the Pitt-3 accoustical generator for resuspending respirable cotton dust could be greatly improved when the generator was driven at its lowest resonant frequency. By operating the generator under these improved conditions and by using an operator controlled feedback loop, we believed a very stable, reliable system, requiring a minimum amount of cotton dust could be developed.