Live rotavirus vaccine candidates representing VP7 serotypes 1, 2, 3 or 4 derived by reassortment between bovine UK rotavirus and human rotavirus strains D, DS-1, P or ST3 were evaluated for safety and immunogenicity in adults, children and infants. Infection was defined by evidence of rotavirus shed in stools or a 4-fold or greater increase in serum rotavirus-specific IgA or IgG ELISA or plaque reduction neutralization antibody. A single oral dose (10(5.3) or 10(5.8) pfu) of reassortant virus was well tolerated and infected most infants: 10/20 (50%) by D x UK; 9/11 (82%) by DS-1 x UK; 8/10 (80%) by P x UK and 13/14 (93%) by ST3 x UK. All 14 infants given two doses of D x UK were infected. These findings demonstrating satisfactory levels of attenuation, safety, infectivity and immunogenicity of each reassortant in infants warrant additional studies of a candidate vaccine containing these four strains.