One case of human infection with Isospora belli and two with I. hominis are described from two counties in Georgia. All of the infections appear to have been acquired locally and two of them were apparently related to an infection in the family dog. Morphologically the species of Isospora found in the human cases was similar to that recovered from the dog, suggesting that two of the human infections might have originated from the dog. However, it is suggested that further investigation is needed to determine if humans can be infected with the Isospora obtained from dogs and if a common source of infection exists for both man and dogs. Since clinical symptoms subsided following the administration of bismuth salicylate in one of the cases, it is suggested that this drug may have value in controlling symptomatic Isospora infection in man.