Hypertension in renal transplant recipients is an important risk factor for graft function and cardiovascular morbidity and mortality. The mechanisms of posttransplant hypertension are not well understood. Most of the time, the nature of this hypertension is multifactorial. Rejection, both acute and chronic, recurrent renal disease, graft renal artery stenosis, native kidney disease and drug therapy with steroids and cyclosporin have all been implicated. Where a single cause can be identified, the therapy can be rational and often very successful. For this reason, the diagnosis of graft renal artery stenosis is important, because percutaneous transluminal angioplasty or surgery can lead to the cure of hypertension and improvement of the graft function. Noninvasive testing, using capto- pril renography for the diagnosis of hemodynami- cally significant renal artery stenosis, presently yields encouraging results. © 1991 by the American Journal of Hypertension, Inc.