The objective of this study is a better understanding of the fate or aerosols inhaled by human subjects. The project has two aspects a) the influence of anatomical and physiological factors on deposition and the utility of deposition studies as tools in the diagnosis of respiratory disease such as emphysema, and b) the development of a simple, rapid screening procedure for measuring aerosol deposition in human populations under circumstances which will make the results applicable to the estimation of dosage rates in working environments. The first phase will employ single breath techniques with breath-holding developed at this laboratory; the second will be based on a new type of apparatus and procedure to be developed for steady state breathing of aerosols. Both phases will utilize personnel and facilities at the N.Y.U. Institute of Environmental Medicine and at the Appalachian Laboratory for Occupational Respiratory Diseases (ALFORD).