This volume represents the proceedings of the Fifth Congress of the International Society of Ocular Toxicology (ISOT), which was held at the Grove Park Inn and Resort in Asheville, North Carolina, October 13-17, 1996. We are delighted to present this volume to the ophthalmic community, especially those with a significant interest in ocular toxicol ogy. The Fifth Congress was developed around themes relating to ocular drug metabolism, the ocular pathophysiological effects of nitric oxide, government issues relating to the use of alternative methods for toxicity testing, and a workshop that encompassed comparisons of both in vitro versus in vivo models as well as different animal models. The outcome of this congress, embodied in this volume, is a contribution to the methodologies currently employed or under development and to various drug or physical effects on different ocular tissues. While the focus of this proceedings is on ocular effects of drugs or other materials, many of the contributions deal with topics that have a much broader interest. The workshop concerning the use of different model systems and the choice of the best animal model for drug testing covers a wide range of interests that ex tends far beyond specific ocular effects. This is especially true in the area of alternative methods and in the choice of the best animal model for examination of different disease entities.