Regardless of different host cells and trypsin addition to inoculum, three rotavirus strains (human rotavirus strain Wa, SA 11 virus, bovine rotavirus) displayed the same features in adsorption, endocytosis at 30 min p.i. and the following steps of morphogenesis. The first progeny virus was regularly observed in the RER cisternae at 5 h p.i. It appears that virus yield enhancement by addition of trypsin was due to a greater number of cells having been infected. The infected single cell did not produce more virus particles. Crystalloid arrangement of provirus particles in viroplasm was only observed with the strain Wa virus. The strain Wa and bovine rotavirus produced intracytoplasmic and intranuclear tubes. SA 11 virus induced only intranuclear striated ribbons.