The serotypic specificities of Gottfried and OSU porcine rotavirus gene 9 probes were investigated in a dot hybridization assay. The probes were reacted with homologous and heterologous serotypes of group A rotaviruses of human and animal origin. Hybridizations were conducted under relatively low-stringency (52 degrees C, no formamide, 5 x SSC) and high-stringency (52 degrees C, 50% formamide, formamide, 5 x SSC) conditions (1 x SSC is 0.15 M NaCl plus 0.015 M sodium citrate). Under conditions of relatively low stringency, the Gottfried and OSU gene 9 probes demonstrated broad cross-reactivity and were useful in the detection of homologous and heterologous serotypes of group A rotaviruses. Under conditions of relatively high stringency, the Gottfried and OSU gene 9 probes were serotype specific. The Gottfried gene 9 probe (serotype 4) hybridized with homologous Gottfried porcine rotavirus as well as the serotype 4 human rotaviruses ST3 and VA70. The OSU gene 9 probe (serotype 5) hybridized with homologous OSU porcine rotavirus and the serotype 5 equine rotavirus H1. Hybridization was not observed with the antigenically distinct group B and C porcine rotaviruses or with other porcine enteric viruses, including calicivirus and a coronavirus, transmissible gastroenteritis virus, regardless of stringency conditions. Analysis of 14 group A rotavirus-positive field samples resulted in the serotypic differentiation, collectively, of six serotype 4 or 5 porcine rotaviruses. No field samples reacted with both the Gottfried and OSU gene 9 probes.