Humans and animals are frequently infected with at least one species of parasite and most also harbour other parasites or infectious agents. The interactions between these agents are often subtle and ignored by parasitologists, ecologists and immunologists. This volume explores these interactions in detail, with particular emphasis on their immunological and ecological aspects. There are also contributions on parasitic infections and AIDS and the problems of treating patients with multiple infections. This volume will be of interest to parasitologists, clinicians, veterinarians, immunologists, ecologists and anyone else dealing with parasitic, viral or bacterial infections in the laboratory or in the field.