Microsporidians are a group of specialized parasites of uncertain taxonomic affinity. Historically considered as members of the Protozoan class Sporozoa, they have been more recently placed in their own Phylum, the Microspora (Sprague, 1977). The Microspora were considered to be primitive members of the Protista Kingdom because while their cellular organization was eucaryotic, they lacked mitochondria. However, Hirt et al.(1997) has demonstrated a gene for a heat shock protein (hsp 70 class) in a microsporidian which is similar to those found in mitochondria. This suggests that the mitochondria may have been secondarily lost in this group, and that the microsporidians are not primitive eucaryotes, just highly specialized ones. Interestingly, this hsp 70 described by Hirt's group is similar to those found in the mitochondria of yeasts. Other evidence is accumulating that suggests that microsporidians may be related to fungi. For example, Edlind et al.(1996) has shown the similarity between the tubulin in microsporidians and fungal tubulin. Also, the production of chitin and trehalose in microsporidians, as well as the structure of thymidylate synthase all suggest a relationship with fungi.