Postnatal development of circadian rhythm in serum cortisol levels in children.

High-pressure liquid chromatography was used to study the development of blood adrenocortical circadian rhythm in a total of 64 children, ranging in age from 1 month to 15 years. Patients with endocrine diseases, congenital anomalies, and diseases of the central nervous system were excluded from this study. Determination of corticosteroid concentration was possible with 20 to 100 microL of serum. Twenty-four hour patterns were determined at six-hour intervals. A distinct circadian rhythm with an amplitude comparable to that of an adult emerged at approximately 6 months of age.