Effect of bilateral adrenalectomy and subsequent injections of hydrocortisone and pentagastrin on the activity of different intestinal digestive enzymes were measured in 20-day-old rats. Eleven days after adrenalectomy the activity of lactase, sucrase, and alkaline phosphatase, but not maltase, was significantly decreased when compared with sham-operated rats. In adrenalectomized rats, repeated injections of hydrocortisone (50 mg/kg) significantly increased the activity of lactase, sucrase, maltase, and alkaline phosphatase by 15%, 49%, 32% and 121%, respectively, over the corresponding adrenalectomized control. Pentagastrin (500 microgram/kg) injections to adrenalectomized rats produced significant 41% and 58% increments in lactase and alkaline phosphatase activities, compared with the adrenalectomized control. Sucrase activity was unaffected by pentagastrin, but maltase showed a non-significant 34% higher activity than in the adrenalectomized control. Adrenalectomy by itself lowered the Km and Vmax of alkaline phosphatase by 33% and 66%, respectively, which were increased to 95% and 70% of the corresponding sham-operated level by either hydrocortisone or pentagastrin treatment. When intestinal homogenates from salinetreated adrenalectomized rats were mixed in equal proportion with homogenates from sham-operated or hydrocortisone- or pentagastrin-treated animals, Km values for alkaline phosphatase were found to be similar to those observed for sham-operated or hormone-treated groups alone. However, in the same mixed preparations Vmax values were found to be additive.