Dot and Northern blot hybridization assays were used to analyze field strains of group A bovine rotaviruses (BRVs) by using nucleic acid probes representing P and G type specificities. The probes were prepared by polymerase chain reaction amplification of hyperdivergent regions of the cloned VP4 (nucleotides 211 to 686) and VP7 (nucleotides 51 to 392) genes from four serotypically distinct (in P or G types) strains of rotaviruses: NCDV (G6, P1), IND (G6, P5), 69M (G8, P10), and Cr (G10, P11). The P and G type cDNA probes were radiolabeled with [32P]dCTP and hybridized with RNA extracted from reference cell culture-passaged rotavirus strains or the field samples. The field samples were obtained from young diarrheic calves from Ohio, Nebraska, Washington State, and Canada. The cDNA probes were specific for their respective G or P types on the basis of analysis of known P and G type reference strains. The G typing analysis of 102 field samples revealed that 36.3% (37 of 102) were G6, 2.9% (3 of 102) were G8, 12.7% (13 of 102) were G10, and 23.5% (24 of 102) were untypeable. The P typing results for 93 samples indicated that 2.2% (2 of 93) were P1 (NCDV-like), 20.4% (19 of 93) were P5 (UK-like), 9.3% (10 of 93) were P11 (B223-like), and 40.8% (38 of 93) were untypeable. This is the first report of the identification among BRV strains in North America of a G type other than G6 or G10. Our report further confirms that G6, P5 rotaviruses are predominant among the BRV field strains that we examined, and the P types of these strains differ from that of the BRV vaccine strain used in the United States (G6, P1). The large number of untypeable G (23.5%) and P (40.8%) types suggests that other or new P and G types exist among BRV field strains.