Murine coronavirus JHM infection in rats can be accompanied by different types of demyelinating central nervous system (CNS) diseases. Infection of suckling rats results in an acute, disseminated encephalomyelitis affecting both neurons and oligodendroglia cells. After an average incubation period of 2–3 weeks, weanling rats develop a predominantly subacute demyelinating encephalomyelitis (SDE) characterized by perivascular cuffings, demyelinated foci, and destruction of oligodendroglia cells, leaving the neurons and axons intact. After 3–8 months, some of the weanling rats which do not after 3 weeks display any CNS affection develop a neurological disease with neuropathological changes similar to SDE. However, in addition to demyelination, remyelination is detectable in this disease pattern. Infectious coronavirus can be isolated from all diseased animals. The infection of weanling rats with coronavirus JHM offers the possibility to explore experimentally the pathogenetic mechanisms responsible for a virus-associated demyelinating process.