Correlation between Banff classification, acute renal rejection scores and reversal of rejection. The Banff classification of acute rejection is based on histologic grades and scores for borderline changes, glomerular, vascular, interstitial and tubular lesions. We reviewed 56 episodes of acute rejection occurring in 44 kidney allograft recipients (30 cadaveric and 14 living donor transplants), comparing Banff classification to degree of reversibility of rejection. Rejection reversal was defined as complete if serum creatinine returned ≤ 25% of baseline, partial if creatinine was > 25% to < 75% of baseline, and irreversible if creatinine was ≥ 75% of baseline or graft loss occurred. Eight biopsies were classified as borderline (SUM score 1.6 ± 0.5), 14 grade I (SUM score 3.3 ± 0.4), 19 grade II (SUM score 4.2 ± 0.3), and 15 grade III (SUM score 8.5 ± 0.4). SUM distinguished borderline and grade III rejections, but not grades I and II. Clinically, grade and SUM score correlated with rejection reversal. Complete reversal of rejection occurred in 93% of patients with grade I rejection, while 47% of patients with grade III had irreversible rejection. The mean SUM for complete reversal was 3.9 ± 0.34 and was different from SUM of partial (6.0 ± 0.86) and irreversible (8.5 ± 0.93), P < 0.006. Meanwhile, vascular scores were similar for rejections with complete (0.9 ± 0.2) or partial (1.0 ± 0.4) reversal, but significantly higher in those with irreversible rejection (3.0 ± 0.4, P < 0.000). Likewise, mean scores for tubulitis and interstitial inflammation were significantly higher for irreversible rejection. Resolution of rejection by steroids was correlated to low vascular score (steroid sensitive 0.65 ± 0.25 vs. steroid resistant 1.42 ± 0.18, P < 0.01), and low SUM score (steroid sensitive 3.7 ± 0.5 vs. steroid resistant 5.22 ± 0.43, P < 0.04). Neither scores for tubulitis nor interstitial cellular inflammation were predictive of steroid sensitivity. These data demonstrate that Banff scoring has clinical relevance in predicting rejection reversal and has implications to first-line therapy of rejection episodes.