We previously observed a marked diversity of rotavirus strains and a high prevalence of the un- common serotype G9 in a small survey of rotavirus strains collected from six centers in India. In the present study, we characterized a larger collection of strains from children hospitalized with severe diarrhea in seven Indian cities between 1996 and 1998. A total of 287 strains were G and P genotyped by reverse transcription-PCR, and some were further characterized by electrophero-typing and subgrouping. Of the four strains common globally, three were found in only 43% of samples (P[8], G1, 15%; P[4], G2, 22%; P[8], G4, 6%), whereas G9 strains made up 17% of the total. Three different G9 strains were present: a P[8], G9 strain, which displayed the long electro- pherotype and subgroup II VP6 specificity, and two P[6], G9 strains, one with the long electro- pherotype and subgroup II specificity and the other with the short electropherotype and subgroup I specificity. Marked diversity was observed among strains collected from different cities and collec-ted over time. Of the 253 strains that were fully typed, 54 (21%) had a mixed G or P genotype. Serotype G2 strains were detected more often in infections caused by single strains than in mixed infections (P < 0.05), whereas serotype G1 strains were found more often in mixed infections than in infections caused by single strains (P < 0.05). The diversity of rotavirus strains and the high prevalence of mixed infections confirm trends reported earlier. Vaccines under development should clearly target G9 strains, and G9 should be included as one of the common global serotypes.