Additional evidence in support of the hypothesis that a large proportion of pituitary control over pancreatic acini is exerted through the thyroid gland was gained by the colorimetric determination of pancreatic amylolytic activity in surgically thyroparathyroidectomized rats. After surgical thyroparathyroidectomy, with or without concurrent treatment with I131, pancreatic weight was reduced from 889 [plus or minus] standard error 37 mg for controls to 450 [plus or minus]20 mg. The amylolytic activity was reduced from 1.735 [plus or minus] 0.147 mg of glucose released from starch to 1.018 [plus or minus] 0.125 mg/unit weight of pancreas and from 31,293 [plus or minus]3470 to 9139 [plus or minus] 1210 mg for the whole gland. Surgical parathyroidectomy had no effect on pancreatic weight or amylolytic activity.