Severe failure to thrive is an important feature in children with both syndromic and nonsyndromic paucity of interlobular bile ducts (PILBD). Thirteen children age 7 months-11 years with PILBD had pancreatic secretions in duodenal aspirate measured for 40 min after secretin-pancreozymin stimulation, six of these children had chronic diarrhoea. Studies were also performed in seven children age 2-12 years who presented with failure to thrive or nonspecific diarrhoea that subsequently resolved. The results of the control and the PILBD children were similar except in the six with chronic diarrhoea. These children had significant reductions in total volume of duodenal aspirate (p less than 0.05), bicarbonate concentration (p less than 0.02) and output (p less than 0.05), and in lipase concentrations (p less than 0.005). Five of these children have had a reduction in stool frequency and more rapid weight gain since receiving pancreatic supplementation. In children with PILBD and diarrhoea, pancreatic insufficiency may be a contributory factor to poor weight gain. These children may benefit from pancreatic extract supplementation.