Duplex Doppler examination of a perinephric abscess in a renal transplant. Perinephric abscess has no characteristic ultrasonic appearance or location. Differentiation from urinoma, lymphocele, or hematoma depends on clinical and laboratory findings. Therapy consists of percutaneous catheter drainage, surgical drainage, and antibiotic therapy. Acute rejection is the most common cause of decreased diastolic flow during the immediate postoperative period. Acute tubular necrosis does not usually alter blood flow unless it is severe. Duplex doppler ultrasonic assessment of the renal transplant during the immediate postoperative period may provide a valuable baseline for comparison if complications develop. Baseline and follow-up ultrasonography to evaluate diastolic flow can help determine whether a posttransplant patient should receive emergency or conservative therapy for complications. 