DNA from cyanelles of Cyanophora paradoxa have a buoyant density of 1.716 g/cm 3. Digestion with the restriction endonucleases Pst I, EcoR1 and Hind III, produces fragments which have been sized by agarose gel electrophoresis. The genome size of the cyanelle DNA, from these data is estimated to be 1.1 × 10 8 daltons. A mixture of RNAs, isolated from purified cyanelle ribosomes, has been localized on an EcoR1 restriction endonuclease digestion pattern and shows binding to eight fragments. These data indicate that genetically, the cyanelles more closely resemble plant chloroplasts although structurally they resemble blue-green algae.