The value of color Doppler ultrasound in the renal transplant follow-up has been evaluated. To do so we used a standardized protocol of analysis on a group of 86 outpatients with different transplant ages and a good and stable graft function defined as a plasma creatinine level < 105 microM/l. Renal volume increased after transplantation and averaged 198 +/- 54 cm3. The graft volume was positively related to the transplant age (p = 0.04). Mean renal blood flow/1.73 m2 body surface area was 301 +/- 98 ml/min, a value at the lower limit of normality. A statistical inverse relationship between renal blood flow and transplant age was found (p = 0.04). Renal vascular resistances increased along with the transplant age (p = 0.003). Renal function evaluated by creatinine plasma levels and creatinine clearance values did not show any statistical correlation with color Doppler findings in normal grafts. In conclusion, ultrasound measures allow us to obtain more sensitive information about the graft status and might be used for a better evaluation of the transplant follow-up.