Shrinking ecosystems concentrate both individuals and species into restricted areas, promoting transmission and exchange of parasites. Fragmentation increases edge and brings an influx of new species into the disturbed or agricultural habitats between fragments, introducing new parasites and possibly leading to the development of new and more pathogenic strains of parasite. Environmental contaminants act as stressors, and may compromise immune systems. Global climate changes challenge the adaptability of organisms, and may allow the invasion of new parasites. Because each of these effects increases the potential for parasites to become pathogenic, the importance of disease is expected to increase in shrinking ecosystems, with the emergence of new diseases and increasing numbers of epidemics. Increased pathogenicity of generalist parasites may pose a threat to species with restricted distributions or small populations. Keywords: climatic change, contaminants, disease, endangered species, fragmentation, new diseases, parasites.