Rotaviruses were isolated on BSC-1 cells from counterimmunoelectrophoresis and/or electron microscopy positive intestinal contents from two asymptomatic and six diarrheic calves from Quebec. The plaque assay was performed using these lines and agar overlay medium containing trypsin and DEAE-dextran. This assay was used to compare the Quebec isolates to an attenuated American strain (NCDV) and another strain (TH) obtained from France. The NCDV strain produced plaques that were significantly larger than those produced by the TH strain. Three Quebec isolates produced plaques similar in size to TH strain, one isolate was similar to NCDV strain and another isolate produced larger plaques than those of both NCDV and TH strains. The other isolates induced the production of plaques that were not significantly different from those of NCDV or TH strains.