Purpose: Adrenal venous sampling (AVS) is limited by technical failures that result from incorrect catheter placement or failure to catheterize the right adrenal vein. The existence of an inadequate sample may not be recognized at the time of the procedure, which can lead to nondiagnostic results. Rapid assay of serum cortisol levels allows for intraprocedural evaluation of the ratio of adrenal and peripheral cortisol concentrations and confirmation of adequate sampling., Materials and Methods: Retrospective review was performed of 64 AVS procedures, 36 performed with digital subtraction venography (DSV) guidance alone and 28 performed with DSV guidance plus intraprocedural quantitative determinations of plasma cortisol levels., Results: Technical success was achieved in 26 of 28 procedures (93%) that included intraprocedural cortisol measurements in addition to DSV. Analysis of cortisol ratios (adrenal vein cortisol level divided by inferior vena cava cortisol level) revealed technical success in 29 of 36 procedures (81%) that used DSV alone (P = .16). Procedure note indication of successful/unsuccessful sampling coincided with cortisol ratios in 28 of 28 cases (100%) that included cortisol measurement and 29 of 36 cases (81%) that did not (P = .01).The feedback provided by the measurement of cortisol levels allowed the operator to salvage three of five inadequate AVS procedures (60%), increasing the overall technical success rate from 82% to 93%., Conclusions: Intraprocedural measurement of cortisol with rapid results allows for prediction of successful adrenal vein catheterization, which may increase the technical success rate of AVS., (Copyright © 2011 SIR. Published by Elsevier Inc. All rights reserved.)