Variations in the electrophoretic pattern (elecrtrophoretype)of rotavirus RNA has been described. The clinical significance of this finding is not clear. The frequence of different electrophoretypss detected on stool samples from children under two years old with RV infection was studied. Fourty eight different electrophoretypes were detected among 283 RV isolated, without predominance of any electrophoretype for severe diarrhoea cases. RV mixed infections, i.e. two different electrcphoretypes during one infectious episode, were found in 29/168 patients (17%) with four or more serial stool samples. 6/16 cases were admitted with mixed infection and 10/16 cases acquired it at the hospital. Among 13 ambulatory cases, the mixed infection was detected in the first stool sample on 8 and after ths third sample on 5 cases. The mixed infections were not more severe and they resulted from association of electrophoretypes long-long (10), long-short (16) and short-short (3). The great variety of electrophoretypes discard the presence of an “hospital reservoir” of RV. There is no relationship between simple or mixed electrophoretype and severity of RV infection.