Changes in nuclear structures have been followed in oocytes of adult minks, from the primordium follicle stage to the Graaf vesicle stage. The followed dynamics well compared with what has been known for other mammals studied. With the mink oogenesis, an intensive production of nucleolus-like bodies occurs: these may be as many as 100 per nucleus. On later stages of occyte growth, ring-like extranuclear bodies were found which have not been observed for other mammals. With the mink, karyosphere formation is generally similar to that in other mammalian species examined, being, however, observed a bit earlier than usually, i.e. on the stage of multilayered follicle with the antrum. Due to this fact, the karyosphere, with the mink, persists longer. With the mink, contrary to other species examined, the formation of the karyosphere as a dense Feulgen-positive body is not accompanied with a total disappearance of the nuclear envelope and nucleolus-like bodies.