Using solid-phase immune electron microscopy, 126 of 129 human rotavirus (HRV) strains could be serotyped directly in stools collected in Italy during the period 1981-1985. Prevalence was 70.5 per cent for serotype 1, and 13.2 per cent for each of serotypes 2 and 4. No serotype 3 strain was detected. In parallel, for 39 of 61 HRV strains tested the electropherotype of genomic RNA was successfully determined. Different electropherotypes were detected among strains of the same serotype, whereas the same electropherotype was found in HRV strains of different serotypes. Serotyping and electropherotyping of HRV strains appear to be complementary to each other, and both should be used in conjunction for epidemiological surveys.