Currently fewer than ten centers in the United States have sufficient technical expertise with inferior petrosal sinus sampling (IPSS) to ensure reliable results. This proposal to develop jugular venous sampling (JVS) with CRH stimulation as a test for the differential diagnosis of Cushing syndrome would potentially contribute greatly to the medical care of patients with Cushing syndrome, as a less costly, safer and more widely available alternative to inferior petrosal sinus sampling. Initial data from 35 patients undergoing both JVS and IPSS revealed no technical problems with either procedure. IPSS correctly identified 28/31 patients with Cushing disease, while JVS correctly identified 23 of these patients using conventional criteria (petrosal:peripheral greater than 2 before or 3 after CRH administration). Thus, JVS may be a useful initial procedure at institutions where IPSS is not available. However, since it is likely that jugular:peripheral ratios will be lower in patients with ectopic ACTH secretion (so far, 1.2 - 2.04), the protocol evaluates also the performance of JVS in patients with ectopic ACTH secretion to determine whether the criteria for interpretation of JVS should be different than those used for IPSS.