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The mechanisms of increased growth of small piglets following split weaning were studied using a total of 10 sows and 100 piglets. Sows and their litters were allocated to a treatment group (piglets split-weaned) or control group (no piglets split-weaned). At day 22 of lactation, piglets in each litter were classified as either 'heavy' or 'light', with equal numbers in each group. 'Heavy' piglets were removed from sows at day 22 (s.e.m. 0.17) in split-weaned litters while 'light' piglets remained with their mothers for an extra week. At 29.5 (s.e.m. 0.21) days of age, sows from both split-weaned and control litters were weaned. Milk consumption was estimated between days 16 and 19 and on day 24 of lactation by weighing piglets before and after sucking. During milk letdown, the teats that piglets sucked from were noted. A video recorder was used to determine the frequency of natural sucklings, the proportion of unsuccessful sucklings, and the time taken for piglets to consume milk during ejection, over a 16-h period before and after split weaning. 'Light' piglets in split-weaned litters grew 61% faster (P < 0.001) than their counterparts in control litters and were 15% heavier (P < 0.01) at weaning. This was explained by a 49% increase in milk intake (64 v. 43 g/sucking, P 5 0.001). Increased milk intake was due to multiple teat swapping with an associated longer duration of sucking during letdown. 'Heavy' piglets weaned at 22 days were lighter at 29 days than their counterparts in control litters (P < 0.01). Gains in growth made by 'light' piglets in split-weaned sows over their counterparts in control litters had disappeared by the time pigs were 9 weeks old, and piglets classed as 'heavy' at day 22 of lactation remained heavier ( P < 0.001) at 62 days of age irrespective of treatment.