A survey of domestic ducks in Emmet and Cheboygan Counties, Michigan, was conducted during the summer of 1948 in order to determine the incidence of infection with Leucocytozoon simondi. The infection was not found in any of the 43 ducks examined during the latter part of June, but was found in all but one of 38 ducks by early August. Successful transfer of the disease by means of inoculation of tissues from "donor" ducks during the acute phase of the disease is again reported. Epizootiological considerations suggest the possibility that early wild duck transients or birds other than ducks may serve as the reservoirs for the infection in the area. The possibility of fluctuation in gametocyte level is suggested. Two cases of infection with Haemoproteus in the domestic White Pekin duck are recorded. It is believed that this constitutes the first such report in this country.