1. Pancreatic growth was measured in rats by changes in pancreatic weight, nucleic acid content and protein content after feeding diets of heated soya-bean flour (HSF), raw soya-bean flour (RSF), 200 g raw soya-bean flour + 800 g heated soya-bean flour/kg (80 HSF) and 400 g raw soya-bean flour + 600 g heated soya-bean flour/kg (60 HSF) for periods up to 36 weeks. Control rats of comparable age to soya-bean flour-fed rats were continued on rat cubes during the 36-week study. 2. Cube-fed rats remained significantly heavier than rats fed on soya-bean flour diets. Analysis of variance showed rats fed on HSF were significantly heavier than RSF-fed rats and rats fed on 80 HSF significantly heavier than those fed on 60 RSF. 3. Pancreatic indices in HSF-fed rats were similar to comparable control rats. 4. Hypertrophy was found in rats fed on the RSF-containing diets with the extent of enlargement corresponding to the RSH content. Hyperplasia was also found in rats fed on RSF and 60 HSF. 5. The greatest pancreatic growth was seen in RSF-fed rats with all the indices peaking at 8 weeks followed by a decline and then a rise again at 36 weeks. 6. The fall in pancreatic indices in rats fed on RSF for 12 and 24 weeks is most likely an effect of general malnutrition due to the multiple deficiences in amino acids which occur in animals fed on RSF. The rise at 36 weeks may reflect increased body growth or the beginning of adenomatous changes.