ABSTRACT We evaluated the growth and function of 21 pairs of en bloc infant kidneys transplanted into adult recipients. Serum creatinine, 99m technetium-diethylenetriaminepentaacetic acid glomerular filtration rates, kidney volumes and resistive indexes were determined at 1 to 3, 3 to 6 and beyond 6 months, and compared using repeated measures analysis of variance tests. En bloc kidneys grew at a statistically significant rate (p <0.001), for example nearly 2-fold in 3 to 6 months (209 +-/69 cc from 132 +-/70 cc), and approaching 3-fold at 6 months and longer (325 +-/106 cc). Similarly, the glomerular filtration rates increased almost 4-fold (83 +-/52 ml. from 23 +-/11 ml. per minute) and 5-fold (121 +-/45 ml., p <0.001), respectively, during the same periods. Resistive indexes remained at normal range (0.60 to 0.63). Recipient blood pressure was normal. Our study shows that infant en bloc kidney transplants grow rapidly and provide excellent function to the adult recipient.