In July 1998, Cortef oral suspension (Pharmacia & Upjohn) was reformulated changing the suspending agent tragacanth to xanthan gum. We subsequently observed suboptimal control of hormone levels in a group of children with classic congenital adrenal hyperplasia, despite increasing doses of Cortef suspension and stringent instructions to parents regarding shaking of the bottles of medication. Nineteen children receiving Cortef and fludrocortisone therapy were changed to hydrocortisone tablets and fludrocortisone, with a 10 percent reduction in hydrocortisone dose. A significant decrease in 17-hydroxyprogesterone (235 +/- 120 vs. 27 +/- 7 nmol/L; p