Color Doppler sonography has been introduced for graft monitoring after renal transplantation. Little is known, however, about independent factors that have an impact on intrarenal Doppler indices as indicators for transplant dysfunction. Therefore, in this study, potential determinants of the resistive index (RI) and of the pulsatility index (PI) in 110 patients with stable renal allografts were studied. The mean RI and PI were 0.70 +/- 0.07 (range, 0.53 to 0.88) and 1.36 +/- 0.21 (range, 0.91 to 1.98), respectively. In multivariate regression analysis, RI and PI correlated significantly with age and arterial pulse pressure of the recipient. There was no correlation with donor age, heart rate, mean arterial blood pressure, and cyclosporine trough levels. Furthermore, parameters of kidney function, such as serum creatinine concentration, creatinine clearance rate, 51Cr-ethylenediaminetetraacetate clearance rate, and proteinuria, showed no significant correlation with the Doppler indices. The data indicate that intrarenal Doppler indices of the grafts are hemodynamic indices, primarily depending on the recipient-related vascular compliance rather than on the function of the graft. Therefore, only intraindividual comparison of the Doppler indices may be useful to detect potential changes of graft resistance during long-term follow-up.