We examined hypothetical relationships between blood parasite infection in Purple Martins Progne subis and extra-pair paternity of males, feeding performance of parents of both sexes, and mate-guarding intensity of males. We found no evidence that infection with either of two parasites, Haemoproteus prognei and an unspecified microfilariad, affected extra-pair paternity. Infected males were no more likely than uninfected males to be cuckolded, and infection did not preclude extrapair fertilization success. Infection also was unrelated to provisioning rates by adult males and females and to mate-guarding intensity by males. However, subadult females provisioned significantly less when infected with Haemoproteus, suggesting that young females have a lower resistance to parasites than adult females, or males.