The NATO Advanced Studies Institute series "Targeting of Drugs" was originated in 1981. It is now a major international forum, held every two years in Cape Sounion, Greece, in which the present and the future of this important area of research in drug carriers is discussed in great depth. Four previous ASls of the series dealt with drug carriers of natural and synthetic origin, their interaction with the biological milieu and with ways by which the latter influences such interaction. The present book contains the proceedings of the 5th NATO ASI "Targeting of Drugs: Optimization Strategies" held in Cape Sounion during 24 June-5 July, 1989. A logical sequel to the last one, the ASI deals with strategies by which milieu inter- ference curtailing the function of drug carriers is circumvented or removed. We express our appreciation to Drs. R. Langer and E. Tomlinson for their valuable advice throughout the planning of the ASI and to Dr. G. Deliconstantinos who, as Chairman of the Local Committee contributed so effectively to its success. The ASI was held under the sponsorship of NATO Scientific Affairs Division and co-sponsored and generously financed by Smith Kline French Laboratories (now SmithKline Beecham), Philadelphia, USA. Financial assistance was also provided by CIBA Geigy (Horsham), Schering (West Berlin), Farmitalia Carlo Erba (Milan), Liposome Technology Inc. (Menlo Park), Pfizer (Sandwich), Dior (Paris), Syntex Research (Palo Alto), ICI Pharmaceuticals (Mereside), Boehringer (Mannheim) , Wyeth (Taplow), Merck Sharp Dohme (Rahway), Sandoz A.G. (Basle) and Lilly Research Centre Ltd.