A patient with bilateral adrenal hyperplasia, due to the ectopic adrenocorticotrophic hormone (ACTH) syndrome, received a 3-month course of treatment with 1,1 dichloro-2(o-chlorophenyl)-2-(p-chlorophenyl)ethane (o,p' DDD), which caused adrenal hypofunction requiring steroid therapy. Eleven months later, Cushing's syndrome recurred. His CT scan showed a left adrenal gland that was enlarged and a normal-sized right adrenal gland. However, the NP-59 image showed increased uptake by both glands. Venous effluent was sampled from each adrenal vein. The plasma cortisol level from the left gland was 1392 ng/ml, and that from the right gland was 667 ng/ml. The latter value was not significantly different from the values obtained at peripheral sites (517-744 ng/ml). In the course of recovery from o,p' DDD damage, the ability of the adrenal gland to take up NP-59 may be restored before the return of its biosynthetic and secretory functions. Serial NP-59 adrenal images can anticipate the recurrence of Cushing's syndrome after adrenolytic therapy, thereby permitting early retreatment.