In 127 infants and young children suffering from acute non-bacterial gastroenteritis, diagnosis of rotavirus infection was done by virus detection and serology. Human rotavirus (HRV) detection was performed by direct electron microscopy (EM), conventional immune electron microscopy (IEM) and/or solid phase immune electron microscopy ( SPIEM ); rotavirus antigens were detected by indirect double-antibody sandwich (DAS) ELISA and HRV isolation was attempted in MA-104 or LLC-MK2 cell cultures. HRV serology was done on paired sera from all the patients by the indirect immunoperoxidase antibody (IPA) technique for HRV IgG determination, and by an indirect ELISA method using a purified HRV Wa strain as a solid phase. HRV particles were detected by EM and/or IEM in 53 cases (41.7%) and by SPIEM in 5 additional cases; HRV antigens were demonstrated by indirect DAS ELISA in the same 53 cases, whereas 40 cases (31.4%) were positive for HRV isolation in cell cultures. Sixty-four patients (50.3%) seroconverted by IPA and ELISA, including all the cases (58) positive for rotavirus detection in stools and 6 additional cases. Thus, SPIEM appears to be the most sensitive technique for detecting a few virus particles in stool specimens, but HRV serology is the most sensitive method for diagnosing HRV infections retrospectively, when paired sera are drawn at an appropriate time. However, EM possess the great advantage of detecting in fecal specimens viral agents other than rotaviruses, such as adenoviruses, enteric coronaviruses, small round viruses, astroviruses and others.