Abstract
In yeast it has been reported that some types of erythromycin-resistance are due to cytoplasmic genetic factors, localized in mitochondria (Thomas & Wilkie, 1968; Slonimski, 1969). In view of the current interest in genetical aspects of mitochondria, and the ease with which cytoplasmic heredity can be demonstrated in Paramecium aurelia, some tests have been made to determine whether erythromycin-resistant variants could be obtained in this ciliate and, if so, to determine their genetic basis.