Heating oncornavirus RNAs at temperatures insufficient for complete denaturation results in forms migrating between the native form (vRNA) and the completely denatured form (vRNA) after gel electrophoresis. Intermediate forms from Rous sarcoma virus or murine leukemia virus were isolated after heating of vRNA's at 58 degrees C and sedimenting in sucrose gradients, and at least four intermediates could be identified in each case. Melting of feline virus (RD-114) RNA produced one major intermediate which required a comparatively high temperature to denature, and a second intermediate occurring in conditions of low ionic strength. Although the subunit model for oncornavirus RNA is not excluded by these data, we propose that vRNA, vRNA', and intermediates may be configurational variants of the same molecule, and a monomer model for oncornavirus RNA is presented.