The therapeutic efficacy of hyperimmune bovine colostrum (HBC) from cows immunized with four serotypes of human rotavirus was evaluated in a double-blind, randomized trial in 75 boys, aged 6-24 months, infected with rotavirus diarrhoea. The treatment group received 100 ml of HBC three times a day for 3 consecutive days, while the controls received the same amount of bovine colostrum from significantly shorter duration of diarrhoea than the controls (median 56 versus 72 h (p<0.001); confidence interval of median difference (CI) 8-32 h). Total stool output (g/kg) between admission and cessation of diarrhoea was reduced by 29% in the HBC-treated group compared with controls (median 205 versus 290 g (p=0.04); CI = 1-154 g). In 50% of the children in the study group, diarrhoea stopped by 48 h, whereas 100% of the controls were still suffering from diarrhoea. No untoward effects were noted in either group. Colostrum from cows immunized with rotavirus antigen is clinically effective in reducing the duration and severity of childhood diarrhoea due to rotavirus.