We have evaluated three nucleoside analogues, i.e. ribavirin, 3-(β-D-ribofuranosyl)-4-hydroxypyrazole-5-carboxamide (pyrazofurin), and 5-ethynyl-1-β-D-ribofuranosylimidazole-4-carboxamide (EICAR), for their inhibitory effects on the in vitro replication of various measles (SSPE) virus strains, including wild type strains recently isolated from measles patients, and for their therapeutic efficacy in hamster SSPE model. Pyrazofurin and EICAR were more inhibitory than ribavirin to the replication of various strains of measles (SSPE) virus, in vitro. Ribavirin improved the survival of infected hamsters in a dose-dependent manner by intracranial administration, and ribavirin at a dose of 10 mg/kg/day completely prevented mortality. Pyrazofurin did not improve the survival of infected hamsters at the maximum tolerate dose. EICAR improved the survival by 50% at a dose of 5 mg/kg/day, whereas the survival decreased when the dose increased to 10 or 20 mg/kg/day. Therapeutic efficacy in vivo of pyrazofurin or EICAR was less than that of ribavirin.