The synthesis of M protein of HVJ (Sendai virus) in rat glioma (C6) cells, as has previously been reported, is selectively reduced at a nonpermissive temperature of 39 degrees C. In this phenomenon no difference was found in the viral RNA synthesis and the stability of the viral RNAs between the permissive and nonpermissive temperatures. Oligo dT-selected RNA from the infected cells at either temperature similarly directed M protein synthesis in cell-free translation reactions even if the reaction was performed at 39 degrees C. These results suggest that the restriction of M protein synthesis in C6 cells at the nonpermissive temperature might be due to the inability of translation apparatus to interact with the mRNA coding for M protein.