A population of American kestrels breeding in southeastern Pennsylvania was examined for hematozoa. Haemoproteus tinnunculi infected 17 of 23 (74%) of the adults. Parasitemia ranged from two to 252, with a median of 32 infected erythrocytes per 10,000. Parasitemia and body weight of female kestrels were negatively correlated. This parasite was not observed in the six juvenile or 38 nestling kestrels examined. Trypanosoma sp. was detected by culture in three of seven (43%) adults, but not in the six juveniles and eight nestlings examined.