To the Editor: We read the article by Floyd R. Sallee, M.D., Ph.D., et al. +(1) with great interest. The authors used the growth hormone response to the α₂-adrenergic antagonist yohimbine as a measure of presynaptic norepinephrine activity in a study comparing anxious children with comparison subjects. There are, however, methodological problems inherent in the use of growth hormone as a measure of norepinephrine activity, largely because the release of growth hormone from the pituitary is inhibited by cortisol +(2). The authors appeared to measure a single baseline blood sample for each subject for the estimation of cortisol content and reported that there was no significant difference in baseline cortisol levels between comparison children (mean=6.5 g/ml, SD=2.8) and children with anxiety disorders (mean=9.1 g/ml, SD=8.4). Measuring single blood samples of cortisol is often unreliable, and integrated measures of cortisol output are preferred +(3). In view of the effect of cortisol on growth hormone release, we believe it would be prudent for these authors to examine a robust measure of cortisol as a covariate of growth hormone response. We further suggest that all studies in which neurotransmitter function is inferred from pituitary hormone measures must measure corticosteroids as a potentially confounding covariate.