Abstract 1. 1. Nucleolar RNA has a vectorial turnover with the dense-particulate part at the origin determining either a centrifugal or a centripetal stable pattern. 2. 2. The centrifugal turnover pattern used in this work lends itself to inhibition studies. 3. 3. These studies indicate an extrinsic and an intrinsic nucleolar RNA, the former being chromosomal messenger RNA. 4. 4. Messenger RNA, and not organizer DNA, primes intrinsic nucleolar RNA. 5. 5. Free messenger was directly observed in the nucleus and followed to cytoplasm.