Inhaled particles can cause a spectrum of responses ranging from simple clearance to pathologic reactions, including acute injury and chronic fibrosis. In vivo and in vitro studies of particulate interaction with lung cells has greatly advanced our understanding of the mechanisms of particle health effects (1,2). Methods for studying particulate interaction with lung cells include simple light microscopy, electron microscopy, and flow cytometry (3). Many investigators have used flow cytometry and fluorescent latex beads to study particle-cell interactions. These particles are useful in that particle uptake by lung cells can be exactly quantified by taking advantage of their fluorescent properties (4–7). However, these latex beads can only serve as a surrogate for actual “real world” environmental particulates.