The virion proteins and intracellular polypeptides of the murine coronavirus MHV-JHM have been analysed by two-dimensional fingerprinting of their [35S]methionine-containing tryptic peptides. The analysis shows that the virion proteins gp98, gp65, pp60 and p23 are distinct. Virion protein gp25 has the same polypeptide component as p23, and virion protein gp170 has a polypeptide component related to gp98. The six virus polypeptides synthesized in infected cells, 150K, 65K, 60K, 30K, 23K and 14K are also distinct. The 170K and 98K species, which are produced by processing, are related to 150K. The 25K species is a processed form of 23K. The identity of corresponding species in the cell and in the virion has been shown and a model describing the genesis of coronavirus JHM proteins can now be proposed.