The study of thermal denaturation for molecular complexes formed during interaction between phage MS2 single-stranded RNA and tilorone has been carried out. Both certain increase of Tm (by on 1.1) and the narrowing of complexes melting interval, delta T, (by 5.6 degrees C), have been detected. The value of hyperchromic effect, H, increases twice. The conclusion is made concerning the formation of double-stranded regions in single-stranded RNA molecules in the process of RNA--tilorone interactions. These results are discussed as an additional proof of our previous presumption concerning stabilization of spontaneously forming double-stranded RNA regions by tilorone binding.