We examined 371 wood ducks (Aix sponsa) for hematozoa from two localities in Missouri (USA) in 1989 and 1990. Thirty-seven (10%) harbored one or more species of blood parasites. Haemoproteus nettionis was the most common parasite, occurring in 36 (10%) of the birds. Leucocytozoon simondi was found in two (0.5%) and microfilaria occurred in five (1%) of the wood ducks examined. Infections were more prevalent in adults (18%) than in immature birds (2%). There was no difference in prevalence between sex, location, or year. Based on seasonal prevalence, transmission probably did not occur at either location in the summer. Increased prevalence in the winter samples occurred after northern wood ducks migrated into the sample areas.