The antiviral activity against rotaviruses of three bovine collectins, conglutinin, collectin-43 (CL-43) and bovine SP-D, was examined. As shown by ELISA and Western blot, all three collectins bound to the Nebraska calf diarrhoea virus bovine strain of rotavirus, and specifically to the VP7 glycoprotein. Inhibition by mannose or EDTA confirmed that binding was mediated through the lectin domains of the collectins. Binding resulted in haemagglutination inhibition and neutralization of rotavirus infectivity, CL-43 displaying the highest activity in both types of assay. In contrast, conglutinin was the most potent of the three collectins against influenza virus A/HKx31. Neutralization of rotaviruses by the lectins was dependent on glycosylation of VP7. Furthermore, rotaviruses adapted to growth in Madin-Darby bovine kidney cells, and thus bearing carbohydrate of bovine origin, remained sensitive to neutralization, although slightly less so than virus stocks propagated in the monkey kidney cell line MA104. These findings provide the first description of antiviral activity of collectins against a non-enveloped virus and may indicate a potential role for collectins in host defence against bovine rotavirus infection.