Numerous economic, sociocultural, and health problems continue to impede the optimal progress of many millions of people in the developing countries in tropical and other geographic regions of the world. Thus, tropical medicine has many aspects including parasitology, bacteriology, and virology, environmental sanitation and hygiene, nutrition, pharmacology, immunology, agriculture, eco- nomics, political science, anthropology, sociology, and behavioral sciences. Like the mythical Proteus, the individual dealing with tropical medicine must assume many roles. There is a growing recognition of the unique problems of the tropical countries. This has led to concerted efforts by many international agencies to attempt to obtain new tools to control many of the tropical diseases that have defied previous attempts at large-scale control. The involvement of the world's leading scientists and institutions as well as the best talents and resources of the developing countries themselves has inspired considerable research in tropical medicine with an inevitable exponential growth in publications. The new series Critical Reviews in Tropical Medicine is being launched to provide topical state- of-the-art critiques of selected subjects in this burgeoning field. Authored by active investigators in their chosen topics, these reviews should be useful for all health professionals, social scientists, and administrators involved in planning interventions, both preventive and therapeutic, in developing regions of the world. Contributions included in Volume 1 span parasitology, infectious disease, immunology, gastroenterology, liver disease, and nutrition.