To the Editor.— A variety of technical and medical factors have been identified that may invalidate results of the dexamethasone suppression test (DST). Our unit1,2and other investigators3-5have reported that plasma dexamethasone concentrations were significantly lower in DST nonsuppressors than in suppressors. Since dexamethasone has a reported half-life of approximately five hours,6we investigated the effects of early biophase kinetics on DST results in depressives. Patients and Methods.— Twenty sequentially hospitalized patients of either sex with a major endogenous depression (age range, 23 to 70 years) were studied after informed consent was obtained. They were carefully investigated for medical factors known to confound DST results and were not exposed to drugs that interfere with corticosteroid metabolism. All patients were hospitalized at least five days before the study to avoid acute admission effects on the DST result. On the day of investigation all patients received standard meals