We retrospectively assayed plasma corticosterone (B) in 143 dexamethasone suppression tests (DST) given serially to 19 depressed patients during the course of their hospitalization. A total of 424 blood samples from these 19 patients were analyzed for both plasma cortisol (F) and B. Concentrations of plasma B were not distributed normally. To establish a cut-off point for a positive B value in the DST, we log transformed the values for B to approximate a normal distribution. Using this approach we determined that a value of 1.3 ng/ml is the most sensitive cut-off point for the plasma B-DST in our laboratory. The serial DST's were performed weekly during the patients' stay and plasma B values were compared with plasma F values. Severities were assessed by weekly Hamilton ratings (17 items). In general, the B values closely parallel the F values. The sensitivity of F-DST was 53% (20/38) and the sensitivity was 56% (20/36) for B-DST. During treatment, both B and F normalized in parallel and this correlated strongly with improvements in the patients' severity ratings. These data confirm the fact that plasma B is as good (but not better) a marker for depression as plasma F in the DST.