The fungus Coelomomyces dodgei (Chytridiomycetes: Blastocladiales) has a complex life cycle involving an alternation of gametophyte and sporophyte generations between an intermediate copepod host (Cyclops vernalis) and a definitive mosquito host (Anopheles quadrimaculatus). Detailed knowledge of the life cycle and factors which favor its completion will aid in assessing the role fungi of the genus Coelomomyces may play in mosquito control. During the past year, it was determined that the infective stages of the fungus, i.e., meiospores and zygotes, invade the host by encysting on, and penetrating through, intersegmental membranes. Host susceptibility has been shown to decrease progressively as immature stages develop to adults. A possible explanation for this phenomenon is that as the cuticle of intersegmental membranes becomes progressively thicker with advancing stages of development, it becomes more resistant to fungal penetration. As a result of these studies it has been determined that 48 hr old copepod nauplii, and first or second instar mosquito larvae are optimal host stages to use for studies on the fungal life cycle and bioassays. During the upcoming year studies on fungal penetration will be completed, and the effects of temperature, pH, and ionic concentration on meiospores and zygotes will be determined.