Recently, there has been a lot of effort in scientific community to understand the role of the naturally occurring hormone, dehydroepiandrosterone (DHEA). In order to plan experiments optimally, it is critical first to characterize the diurnal rhythm in healthy individuals. We present analysis of DHEA concentrations under the framework of linear mixed-effects model. The samples were collected over 23.5 hours on 49 healthy individuals (27 young: 15 men, 12 women; 22 elderly: 12 men, 10 women) under placebo and alprazolam (2 mg oral dose) treatments. The population profiles of diurnal variation of DHEA concentrations, specific to age, sex, and minority status, and the effect of alprazolam on DHEA concentrations are estimated.