An atypical group A rotavirus (993/83) was isolated from a 3-day-old German calf with diarrhea. It differed from 35 conventional German bovine rotavirus isolates analyzed previously with respect to subgroup (strain 993/83 was non-subgroup I and non-subgroup II), serotype (strain 993/83 showed a two-way cross-reaction with serotype 7 and a one-way cross-reaction with serotype 3), and electropherotype (strain 993/83 showed comigrating gene segments 10 and 11). Isolate 993/83 reacted with only one of four monoclonal antibodies that recognized a common VP6 epitope(s). In addition, VP6 and VP2 of isolate 993/83 showed one-dimensional peptide maps that differed substantially from the peptide maps of VP6 and VP2 from all bovine rotavirus isolates. By RNA-RNA hybridization, the 993/83 probe failed to react with a panel of mammalian rotavirus strains, including bovine rotaviruses. It hybridized, however, to genomic RNA of an avian rotavirus strain. Isolate 993/83 could thus represent a candidate for a natural interspecies transmission of rotavirus between different classes of vertebrates.