Cultures of human retinal pigment epithelial cells have been challenged with a number of biological (lipofuscin, melanin, and rod outer segments) and non-biological (latex microspheres) particles at a variety of concentrations. The particles were chosen to include examples of both degradable and non-degradable systems. A range of morphological changes were observed by phase contrast microscopy, and these became more atypical with increasing concentration. At the highest concentration cells had ingested so many particles that many had died and others had ruptured. The time course of these changes indicated a relationship between cellular lytic activity and the capacity of the particle to degrade. The potential of this system as a model for studying senescence is discussed.