The DNA in the macronucleus of the protozoan Oxytricha, unlike like that of typical eukaryotes, exists as short, gene-sized molecules. Within the macronucleus the rRNA genes are contained in molecules 7,380 nucleotide pairs in length. This rDNA has been substantially purified by selective denaturation of non-ribosomal DNA followed by S1 nuclease digestion. Results from restriction nuclease digestion and rRNA:DNA hybridization who that the rDNA is a linear, non-palindromic molecule which contains one gene each for the 19s and 25s rRNAs. A total of less than 600 base pairs of DNA lies between the 19s and 25s genes or at the 3' end of the 25s gene. The non-coding portion of the ribosomal DNA is almost entirely limited to an approximately 1,400 base pair region at the 5' end of the molecule.