The efficacy of hyperimmune bovine colostrum received from cows immunized with simian rotavirus SA11 in the treatment of rotavirus gastroenteritis was compared in a randomized double-blind trial to colostrum and ordinary milk preparations. One hundred and thirty-five children aged 6-30 months with rotaviral gastroenteritis received either hyperimmune bovine colostrum (n=42), ordinary colostrum (n=42) or milk (n=41) as a 100 ml solution four times/d for 4 d. Even though the differences were in favour of hyperimmune bovine colostrum in all the variables evaluated [greater weight gain (403 vs 343 g), shorter duration of diarrhoea (3.1 vs 3.6 d), fewer stools during 6 d (11.5 vs 13.6) and fewer stools during the first 3 d (9.3 vs 11.3)], all the differences were statistically insignificant. Differences of this size are clinically unimportant in well-nourished immunocompetent children, but we suggest that the hyperimmune bovine colostrum tested in our trial had some effects in the treatment of acute rotaviral gastroenteritis and should be evaluated further.