The objective of this program is to provide information on the differences between vertebrate and invertebrate stages of animal parasitic hemoflagellates and to gain an understanding of the transformation process between these two stages. This involves a two- fold research program. First is a study on the nutritional and environmental factors that are important for (1) growth of the invertebrate stage in defined media, (2) growth of the vertebrate stage in axenic culture and (3) the effect that these may have upon transformation. Second is a comparative study on the metabolic differences between the two stages.