The RNAs of transformation-defective (td) deletion mutants of the Schmidt-Ruppin strain of Rous sarcoma virus were found to vary in size when compared by polyacrylamide gel electrophoresis. Three of seven td mutants appeared to recombine with a mutant of Rous sarcoma virus (Schmidt-Ruppin), which has a temperature-sensitive sarcoma (src) gene and is termed ts68, to give rise to recombinants with a reduced temperature sensitivity. The results suggested that different clones of td mutants exist: some in which the src gene appears to be deleted, and others in which the src gene is only partially deleted. A direct correlation between RNA size and the extent of src gene deletion measured by recombination was not obtained, possibly because the recombination assay could only detect src sequences homologous to the lesion(s) of ts68, whereas the electrophoretic analysis of the RNA measured src deletions as well as other possible alterations of the RNA.