In adults, morning plasma cortisol levels are twice that of late afternoon and evening values. In children, a delay in the time of onset in peak cortisol levels has been observed in those treated with inhaled corticosteroids. Consequently, the single morning cortisol level has a low sensitivity for detecting adrenal insufficiency in children. It is not clear which test is best for detection of clinically relevant hypothalamic-pituitary-adrenal (HPA) axis suppression in children; 24-hour plasma cortisol is a good test because it measures biologically active, free cortisol levels for the entire day and is noninvasive. For research purposes, the 24-hour integrated concentration plasma cortisol test is preferred. Studies that have looked at HPA axis suppression with intranasal corticosteroids indicate that overall, intranasal corticosteroids have minimal effect on the HPA axis. A review of the literature reveals one study in which there was a decreased output of urinary cortisol during treatment with either budesonide or fluticasone propionate in adults. Other studies of fluticasone propionate or budesonide have shown no effect on the HPA axis in children. Beclomethasone dipropionate was shown to affect urinary cortisol output in one study of healthy volunteers. However, in a long-term study in children, no effect on the HPA axis was found. Mometasone furoate has been extensively studied in more than 20 trials of adults and children. No effects on the HPA axis were detected in either children or adults. It is unlikely that children are more sensitive to corticosteroids than are adults. There seems to be little point in performing routine monitoring of adrenal function in children who are treated with intranasal corticosteroid treatment.