One strain of human rotavirus subgroup 1 (KUN) and one strain of subgroup 2 (MO) were isolated with the MA104 cell line, a fetal rhesus monkey kidney cell line. Their subgroup specificities and RNA patterns were identical to those of rotaviruses present in stools before cultivation. Distinct cytopathic effects consisting of obscure cell boundaries, cell fusion, cell rounding, cell detachment, and lytic foci were recognized at passage 3 of MO and passage 6 of KUN. No differences in cytopathic changes were found between the two isolates.