Trichomonas vaginalis virus is a double-stranded (ds) RNA virus found in the parasitic protozoan T. vaginalis. To examine the possible existence of related viruses in various T. vaginalis strains and isolates, we screened 20 such isolates and found the characteristic 5.5-kb viral ds RNA in 16 of them. An additional 0.5-kb ds RNA band was also identified in 10 of these virus-infected T. vaginalis isolates. In a local isolate T1, this 0.5-kb ds RNA cross-hybridized with the 5.5-kb ds RNA. Preliminary evidence from CsCl buoyant density gradient centrifugations suggests that the two ds RNA species are encapsidated in separate viral particles by the same capsid protein. The 5.5-kb ds RNA in isolate T1 exhibited moderate hybridization with the prototype 5.5-kb ds RNA in T. vaginalis stratin NIH-Cl. Little cross-hybridization was observed among the 5.5-kb ds RNAs from T. vaginalis isolates JH32A No. 4, T1 and T5, although the viral proteins in these isolates are of similar molecular weight and share common epitopes as viewed by Western blotting. Hybridization characteristics of the 5.5-kb ds RNAs in individual isolates were further analyzed, and the results suggest great ds RNA divergence among the T. vaginalis viruses. Interestingly, the 0.5-kb ds RNA in different isolates of T. vaginalis also exhibited divergence in patterns closely associated with that of the 5.5-kb ds RNA.