A Phase 2, crossover pharmacokinetic and pharmacodynamic study in 16 adults (8 females) with classic CAH, comparing a newly-developed modifed-release formulation of hydrocortisone with conventional hydrocortisone, was completed. This newly developed formulation of hydrocortisone, Chronocort, was designed to mimic the normal cortisol circadian rhythm. Twice daily Chronocort was found to approximate physiologic cortisol secretion. Compared to conventional therapy at baseline, Chronocort at 6 months showed improved androgen levels throughout the day and this lowering of androgens was achieved with a lower or similar average daily glucocorticoid dose. Although there were no significant changes in body mass index, studies of body composition showed an increase in lean mass (females) and a decrease in fat mass (males). This novel hydrocortisone formulation represents a new treatment approach for patients with CAH and will be studied in a multi-center phase 3 clinical trial.