At non-permissive temperature viral specific RNA synthesis was not restricted in rat glioma (C 6) cells infected with HVJ (Sendai virus) wild-type. However, as has previously been shown (J Gen Virol [1984] 65: 639-643), the synthesis of M protein was reduced at non-permissive temperature, in contrast to the L, P, HN, Fo and NP proteins which were synthesized in comparable amounts at permissive and non-permissive temperatures. In this report we show additionally that viral nucleocapsids (NC), which consist of L, P and NP proteins, were formed within the infected cells at both temperatures. Hemagglutinin and neuraminidase activities were also detected in samples incubated at non-permissive temperature. By membrane immunofluorescence and cell-surface immunoprecipitation it was shown that migration of HN and Fo proteins to the cell surface occurred normally at non-permissive temperature. Additionally, the L, P and NP proteins, which were associated with the plasma membrane isolated from the infected cells maintained at permissive temperature, were absent from the membrane of cells incubated at non-permissive temperature. These results suggest that NC and glycoproteins synthesized at non-permissive temperature could not assemble effectively at the plasma membrane because of a lack of M protein. Thus, the host-dependent ts lesion of HVJ in C 6 cells was considered to be mainly in M protein synthesis.