Four different methods of quantifying the 1-mg Dexamethasone Suppression Test (DST) were contrasted with serial testing in endogenous depressives receiving electroconvulsive therapy (ECT). Of three continuous measures in 38 patients with pretreatment DSTs, only the log-transformed value for plasma cortisol was normally distributed, indicating that it possessed superior psychometric properties. Pretreatment Hamilton Depression Rating Scores (HAM-D) correlated positively with pretreatment DST status, with a similar association noted between posttreatment DST status and HAM-D scores. There was no uniform effect of ECT on the DST. Although pretreatment nonsuppressors showed a trend toward decreased postdexamethasone cortisol values, initial suppressors (cutoff: 5 micrograms/dl) evidenced a significant increase in these values, and 35.3% of initial suppressors were nonsuppressors at final DST assessment. These trends were noted in the DST assessment done following the third ECT treatment, suggesting an effect of regression to the mean. The findings highlight the importance of following initial DST suppressors in studies of this type.