The present study was designed to evaluate the differential effects of dietary glucose, lactose and starch on small-intestinal morphology, organ weights, pH of chyme and haptoglobin levels in blood plasma of weaned piglets. It was hypothesised that lactose consumption would ameliorate the weaning-induced decrease in gut integrity. A total of forty-two barrows were used. Piglets were weaned at 27 (sd 0·8) d of age and weighed 8·0 (sd 0·51) kg. On the day before weaning (day −1) all pigs were blocked according to body weight and randomly assigned to seven groups (n 6 per group). The groups differed in diet and day of dissection. On the day of weaning, dissection was performed on one group of six piglets. The remaining groups were fed one of three experimental diets in which glucose, lactose or starch had been iso-energetically exchanged, supplying 24% dietary energy. The piglets received a liquid diet (air-dry meal:water of 1:2, w/w). The piglets were given access to a maximum of dietary energy in order to prevent confounding between feed intake and villus architecture. The piglets were dissected and sampled on days 0, 3, or 10 post-weaning. The results show that the carbohydrate source did not affect growth performance, organ weights, villus architecture, pH of chyme and plasma haptoglobin level. The weaning transition resulted in decreased villus height and increased haptoglobin levels. In the contents of the caecum and large intestine, the pH decreased after weaning. It is concluded that at least under conditions of similar feed intake and low infectious pressure, dietary lactose does not ameliorate the weaning-induced compromise of small-intestinal integrity when compared with either glucose or starch.