The genetic complexities of several ribodeoxyviruses were measured by quantitative analysis of unique RNase T1 resistant oligonucleotides from 60-70S viral RNAs. Moloney murine leukemia virus was found to have an RNA complexity of 3.5x106 daltons, whereas Moloney murine sarcoma virus had a significantly smaller genome size of 2.3x106. Reticuloendotheliosis and visna virus RNAs had complexities of 3.9x106 and 3.5x106, respectively. Analysis of RNase A resistant oligonucleotides of Rous sarcoma virus RNA gave a complexity of 3.6x106, similar to that previously obtained with RNase T1 resistant oligonucleotides. Since each of these viruses was found to have a unique sequence genomic complexity near the molecular weight of a single 30-40S viral RNA sub unit, it was concluded that ribodeoxyvirus genomes are at least largely polypoid.