ABSTRACT: A low intensity Steinhausia-like infection was observed in histological sections of the gonads of 7 out of 10 female Sydney rock oysters Saccostrea commercialis obtained from a farm in Queensland, Australia. Parasitophorous vacuoles occurred within the nucleus and cytoplasm of ovocytes and contained up to 18 unicells (in cross section). Infection caused an intense hemocyte infiltration. The parasite may cause problems in S. commercialis culture at higher infection intensities.